The developer preview is just that: a preview. It's pretty much the same version that will officially be going out in just a months time. Only difference will be bug fixes, minor optimizations and stability improvements. Other than that, what you see now is what you'll be getting in a month's time (well, unless your carrier decides to postpone the update for ages, which it most likely will).
Other improvements, however, not included in this preview would be firmware improvements, such as Nokia's Bittersweet Shimmer. Those are separate, and will be shipped out along with the official release of GDR3 (once your carrier approves it, of course, which could take ages).
On a separate note, loving GRD3 on my Lumia 1020 thus far. Makes an already great phone better, especially rotation lock and the new way of force closing apps! Sure, that's old news on other platforms, but it's nice Microsoft FINALLY caught up. Plus, I'm also celebrating that we now have a way of updating outside the carrier's evil clutches. Hip hip, HURRAY! This will definitely hold me over until Windows Phone 8.1/Blue in January.