The future for the N8x0 devices is community support via Mer. There may be some community bug-fixes for Diablo too, but I think the more promising direction is Mer.

Hopefully Mer will bring some of the newer Fremantle goodness to the older devices, but we'll have to be realistic about graphics performance.

Fremantle is Maemo 5, and it won't run on older devices. Mer can hopefully deliver on enough compatibility with Maemo 5 that apps without intensive graphics need will work (my guess is as a recompile, not binary compatible, but that's only a guess.)