4th edition? I really hope it isn't like Saga. I like the complexity and obscurity of D&D. I had exhausted all the interesting builds in Saga in about a week of getting the book. And there are several significant rules changes that don't make sense, such as a full round action including your swift action, that wouldn't work well with certain D&D paradigms.
Static defense would also be a big problem if they kept iconic spells such as fireball around. Imagine you nuke a bunch of orcs and tank your roll. They all count as having made their save, as opposed to the current system where it would average out as the orcs each rolled a save. It would be a time saver, to be sure, but I would feel pretty gypped playing a caster if that were the case.
Another thing I really hope they avoid is the consolidation of classes into generic fighter/caster/skillguy. And then all fighters/caster/skillguys have the same base stats with only talents to differentiate them. And I really hope they don't go with Skills using the same resource as Feats as you gain levels.
There are things I liked about Saga though. The skill consolidation made sense, though pretty much anyone I've talked to went further and clumped climb, jump and swim into a skill called athletics. I liked the extra hitpoints at first level, so you can actually take a hit. Though I would have gone with a flat 20 point bonus rather than with 3xHD, so the d6 classes wouldn't have as big a gap between them and the d10 classes.
I think the people who enjoy lots of role-playing with lite rules should play another system. When I want that kind of experience that's what I do. I really enjoy Riddle of Steel and the various incarnations of the White Wolf games. And when I want to challenge myself to build interesting characters that take advantage of obscure synergies I play D&D and I love it. I hope they took gamers like me into account when designing the new system. I'd be really disappointed if everything got too simple.