My reasonable hopes for 4th Edition (not that I want it, I like 3.5 very much, thank you, but if WotC must it eventually, here's some things I'd like to see).
Continued d20 mechanics/OGL support. It makes it easier on the fans to share their home-brew stuff on the web, and arguments in other threads aside, it is apparently at least not hurting WotC (or they probably wouldn't have SRD'd 3.5, & d20 Future for example).
A spontaneous divine caster core class. It will probably be Favored Soul, but I'd rather it be the Mystic from DLCS. I think that the priest who isn't a heavily armored warrior cleric but instead a more spiritual and independent being who relates directly to his deity is a missing archetype in D&D.
Restore Darkness spells to creating inky blackness, not "shadowy illumination". Casting Darkness in a pitch black room shouldn't increase the visibility, fer cryin' out loud!
Personally I'd like to see a Noble core class for PC's more oriented towards political/intrigue characters in games that support that, but I don't see it as very likely.
The Swift/Immediate actions are a good rules tweak that helps the system.
Action Points, as was mentioned they would likely be an optional rule in the DMG. They are already in d20 Modern and Eberron, and are an option in Unearthed Arcana, and are very nice for DM's who like cinematic games where the PC's overcome overwhelming odds.
No Summonable Paladin PokeMount. Druids and Rangers can't summon their animal companions from some mystic elsewhere, why Paladins? It also seems just a little inappropriate for some D&D settings to make the warrior of pure good into a summoner.
Class Defense Bonuses, at least as an option in the DMG, which is another popular rule in d20 games other than D&D, and makes the game less about an arms race of keeping up with neat stuff.
A feat akin to the Ancestral Relic feat in Book of Exalted Deeds (or the Ancestral Daisho of the OA Samurai), where you can have a magic item which gains power as you level up, another piece of making the game less about stuffquest and neat gadgets.
Restore the duration of the ability buff spells to 1 Hour/Level. From what I understand it was nerfed to increase dependence on magic items instead of spells, which again I think D&D shouldn't be about your magic items list.
No new races. I don't want Warforged or Ilumnians in core D&D, neither seems particularly appropriate in my eyes for most settings, and I don't want to have to deal with house-ruling them away (and player whining that I'm restricting their options). While I might like Genasi, Aasimar and Tieflings in my Realms game, I can recognize that they don't belong in the Core, which is supposed to be portable and flexible to many settings.