I think it's possible that a 4e would not be a radical departure from 3.x, just as 1e and 2e were compatable (I've never done a real comparison, having played 1e in the 70s and 2e in the 90s, but I've seen convention games listed with 1st/2nd AD&D in the System line). At least I never noticed any glaring departures, just new stuff, like Proficiencies.
It could hew close to the Star Wars Saga Edition game, which tweaks basic d20 into something more streamlined and more flexible in character creation for choosing your class features.
Even if that weren't the model, I'd imagine not much work to adapt current modules to a new version of D&D.
The question is, would they cancel the OGL? It's theirs, they could pull it if they wanted to, but I don't think it has hurt them, so why not update it and continue...?
Gnome Boy (a.k.a. "Jon") • DCC play-tester @ DDC 35, Feb 2011. • Beta DL 2111, 7:00 AM PT, 8 June 11.Playing RPGs since 1977
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