I think you're right,
@M.T. Black, that the big issue is how far designers (and players) are willing to stray from WotC 5E's baseline. Even the wild and craziest 5E material -- the leveless, non-combat spells in Metal Weave's
Incantations, maybe -- are very clearly supplementary to the game in the way it's regularly played.
No one is ripping apart 5E and rebuilding it the way that, say,
Whitehack or the
Black Sword Hack have done in the OSR movement.
Part of that, I suspect, is that the audience is mostly interested in traditional gameplay models. I don't have firm numbers -- if firm numbers can exist without a marketing survey no one would pay for -- but I suspect more folks play pretty traditional D&D style games with OSR retroclones than play the wild and crazy OSR stuff assembled like Lego from its component parts.
Dolmenwood may not use all traditional classes, races, spells and monsters, but no one in 1981 would be confused about how to play it if a copy fell back in time through a wormhole.
I think the 5E chassis is, by and large, the best "advanced" ruleset D&D has ever seen, so there's definitely a lot of good Lego to play with. And I do hope we will see people doing crazy stuff with it. I think it will require designers to blaze a trail by themselves and hope that someone wants to follow, rather than it being the safe commercial path of doing books in the WotC mold. (Tales of the Valiant's deviance from the WotC version of 5E is a matter of degrees, not any major break, by design.)