There's been a lot of request for a farming pack, which is something that's not been done before. That, I think, would need EP-scale development. I don't see EPs going away until there's really nothing left that doesn't need a larger budget because of all the not-visible work that goes into it - the way Cats and Dogs needs a lot of new meshes and animations + new interaction systems.
As for worlds, we've seen full-sized worlds only with EPs so far. GPs have had only mini-worlds. I suspect that, too, comes down to how much budget it takes to make those worlds happen and that without EPs, we'd end up back into separately purchased worlds, but with less new about them than we get with an EP.
