I presume the list of modules they can use is based on what WotC has no interest in using in further Ghosts of Saltmarsh style books, and it's interesting to speculate on what that might entail. However, there are a large number of modules they can still do, either way, it'll be fun to see what they can do to make them interesting.
If we assume that everything from Tales from the Yawning Portal is off the table, as well as the original Ravenloft module, and Ghosts of Saltmarsh (because both WotC and Goodman Games probably don't want two in-print products cannibalizing sales), I don't know that there's really that much left that the audience would consider classics:
A1-4, the Slavers series, seems ripe for The Ghosts of Saltmarsh treatment. It's Greyhawk-based, but it's set in the Pomarj, which is a pretty generic "badlands with bandits and goblins and such" region. I suspect Forgotten Realms fans can think of places to set the adventure before reaching the end of this sentence.
B3, the Palace of the Silver Princess, had a messy path to publication which definitely seems like a subject matter Goodman will want to explore, including very different prints of the adventure. I'd consider this a lock for an upcoming book in this series.
B5-B12 includes some well-liked adventures, like Horror on the Hill, the Veiled Society and Rahasia, but I don't know that any of them has a constituency eager for them to be reprinted or their history explored.
The most prominent C module --
Hidden Shrine of Tamoachan -- was already in Yawning Portal. The next runner up, C2:
Ghost Tower of the Inverness, is a fine but not amazing funhouse dungeon. Geographically, it's located in the neighborhood of the Slaver series, so it might be a good candidate to include in there, much like the Saltmarsh series was fleshed out with other adventures.
No one cares about or misses the
Companion modules. Their only real selling point is that they're rare high level adventures, but they don't seem likely to either get the Saltmarsh treatment or be put in this Goodman reprint series.
The
D series is awesome, but since the Giant series is in Tales from the Yawning Portal, it seems challenging to use them in a reprint product. Maybe WotC might bring them back as part of a Saltmarsh style Underdark book, but the Greyhawk Underdark is a different place from the Forgotten Realms one and is one of the few classic modules that has such a strong tie to its setting. I'd be surprised to see this one come back.
The
DA Blackmoor adventures don't seem like ones WotC wants to call a lot of attention to, given the weirdness between Arneson and TSR over the years. And if Goodman was going to do a Blackmoor project, I suspect they'd be more likely to go back to the original source, rather than reprint the TSR modules.
The
DDA Mystara modules are too obscure and setting-specific to be worth bothering with.
The
Dragonlance modules seem like a great candidate for doing
something with, but it seems like it'd be beyond the scope (and outside of the preferred tone) of the Goodman project. Is this the longest period that Dragonlance has been out of print as a gaming product? It feels like WotC must be working on something ... right?
The
Dark Sun modules probably are pretty interesting historically, but I can't see WotC letting someone else play with those before they get a chance to use them some time.
As I said before, I'm probably close to the entire audience for
EX 1: Dungeonland and EX 2: Land Beyond the Magic Mirror. I'd expect a new third party Lewis Carroll based product for 5E before I'd expect to see these back in print in some fashion. (If someone did a Castle Greyhawk product, though, these and some of the other ephemera would be good to see in a companion volume.)
The
Giant series was in Tales from the Yawning Portal.
The
GA series doesn't have the audience. If we didn't see anything from the Murky Deep in Ghosts of Saltmarsh, we're not likely to ever see it.
The H (or
Bloodstone) series doesn't seem likely to be revisited outside of, maybe, a theoretical mass combat product from WotC. But D&D has moved away from simulating fantasy armies. I think WotC is likely happy to leave this to third party products.
The
HHQ (solo challenge adventures) don't have a big constituency and don't seem like a product that lends itself to giant hardcover phone books, since the interest would be using them at the table. Fans of these should be lobbying third party providers to make new adventures like these.
The HW (
Hollow World) adventures are hyper-specific to their setting, which isn't easily portable to other campaign settings, unless there's a whole lot more hollow worlds out there than we realized.
As I said before, I suspect I6 (Ravenloft) is off the table because of Curse of Strahd. The rest of the line is a real mixed bag. I1,
Dwellers of the Forbidden City is pretty good, although barebones by today's standards. It might be a good basis for a Ghosts of Saltmarsh style product. The
Desert of Desolation modules (I3 through I5) seem like a likely Ghosts of Saltmarsh style product -- in fact, I suspect it's on their shortlist. The rest of the line is ... OK. If anyone is really pining to see a 5E update of Tomb of the Lizard King, I'd be surprised.
The IM,
Immortal series, has the same issue as the COM modules, but only moreso. I mean, yeah, there's very few adventures out there for divinely ascended player characters, but I would expect to see this stuff, at best, used as flavor for 5E epic level rules, like they were for the 3E rules.
I could see L1-3 getting the Goodman treatment, if it wasn't for Leonard Lafofka continuing to turn out new adventures and materials on Dragonsfoot, as recently as five years ago. And only L1,
the Secret of Bone Hill, casts much of a cultural shadow, and it's pretty minor. Again, if it was going to be used, it probably would have been tucked into the Ghosts of Saltmarsh.
M (
Master) series has the same issues as the Companion and Immortal adventures.
The
MV and MSOLO adventures have a very small audience. If they ever came back, I imagined they'd be as an app.
The N series has one beloved module -- N1,
Against the Cult of the Reptile God -- which I wouldn't be surprised to see WotC reprint in some fashion. But the rest of the line runs from unremembered to actively hated.
The two O (
One on One) adventures seem better suited for an app than anything.
The OA (
Oriental Adventures) content seems unlikely to reappear until WotC does a more Asian-flavored book. (And likely they'd ditch "Oriental," which was dated in the 1980s and actively pisses a lot of people off now.) Given that there's an Asian polearm that doesn't appear in the PHB in the Warriors & Weapons Young Adventurers Book, I wonder if something is being developed along those lines now.
OP1,
Tales from the Outer Planes, and Q1,
Queen of the Demonweb Pits, both seem unlikely to be reprinted. OP1, because it's a sort-of-remembered anthology and Q1 because it's so tied to the G and D series.
The R series of
RPGA modules would probably be really interesting to the historical reprint set, especially given that the last few of Frank Metzner's adventures in the series were never published. How large that audience is, though, is probably a problem. The separate RPGA line has similar issues, especially since several of them were reprinted under the main TSR lines.
The three early
Ravenloft modules in the RA series are all setting-specific and just OK. If anyone was going to touch these, it would likely be WotC. I can't imagine this is the way they'd go about expanding Curse of Strahd, though.
The first two S modules are in Tales from the Yawning Portal and S3, Expedition to the Barrier Peaks, is coming from Goodman later this year. S4, the
Lost Caverns of Tsojancth, is fine, but mostly fun because it's a big bucket of new monsters, spells and treasure, plenty of which don't exist in 5E. I suspect WotC would rather just pull content from that as appropriate than do anything with it, though. The final S adventure, Labyrinth of Madness, probably has an audience, but 2E seems beyond Goodman's apparent interest so far and I don't know that it has enough to worry about history-wise. And WotC is capable of making new deadly dungeons if they want to.
I feel comfortable saying that none of the
Spelljammer adventures will get updated without WotC being at the helm.
T1-4 (which really ought to be T1 and T2 ... it's two adventures, the
Village of Hommlet and the Temple of Elemental Evil, man!) does seem like a decent candidate for a reprint. But Gail Gygax's reticence in letting any of Gary's material pass into others' hands makes it hard to see how Goodman would give it the treatment Joseph Goodman would want to and I suspect WotC feels like they've already covered this thematic territory in Princes of the Apocalypse.
The
Saltmarsh series, obviously, is in Ghosts of Saltmarsh.
The
UK series (plus I8, which was produced by that same group) seems like a really good candidate for a Goodman reprint product, for the historical perspective alone, but eight adventures is a
lot. Some of the adventures are well-remembered, though -- Beyond the Crystal Cave, along with Danger at Dunwater, was the first time I remember an official adventure where slaughtering everything in sight wasn't the obvious right choice.
All the
World of Greyhawk adventures seem unlikely to be something Goodman would have access to, between WotC holding onto Oerth for themselves for now and Gail Gygax's discomfort with letting other people look at Gary's archives.
There are a
lot of X modules. X1, the Isle of Dread, has already been published by Goodman. I think X2,
Castle Amber, is a great candidate for another book in the series. After that, though, you run the gauntlet from OK to deeply problematic (I can't imagine anyone will be given the rights to do anything with
Drums on Fire Mountain).
After that, you're out of the classic era. I can't imagine Goodman Games getting excited about anything from the 1990s or later. A lot of the great stuff from that era, like the Planescape books, seem unlikely to reappear outside of a new WotC product.