Frankly, I've been out of step with the scene for the last month or so, so I'm not totally sure what the new developments are shaping up like. Stinebd has
provided the glue to build off the unmodified AOSP sources, so I imagine (/hope) more and more will shift to use that. It's clean, it stays up to date courtesy of the main android devs, and has a minimum of weird, strangely sourced binaries. For the curious,
instructions are here.
I don't know exactly how the AOSP moves, compared to released ROMs, though. As for what version of Android will get the most attention, my guess is on the latest one that's functional, with the others getting a little less. (Though Donut ROMs are still popular on Vogue, so going forward, who knows.)
The kernel, of course, will continue on, separate from all these concerns. There tend to be tweaks necessary for different Android releases, but most of the kernel work helps with all Android versions.