Certainly we've all noticed that WotC is playing with a lot of new subsystems based on "per encounter" rather than "per day" paradigms, and I think that's likely to be a big part of 4E's design philosophy. I'm not sure they're ready to finally kill the diseased old cow that is the Vancian / "fire-and-forget" spell system, but it seems likely that it will at least find itself sharing space with another, less restrictive system, the same way prepared and spontaneous casters coexist now.
At the very least, I'd say that Warlocks--and/or other Warlock-like classes--will make their way into the core system.