I personally prefer a primarily world-painted world, in part because it differs from the regular Minecraft experience and because I get to appreciate someone else's large-scale creative work. Of course, we should also have TC/vanilla regions present for those who prefer that style.
As for specific features in the next rev, I think savannas would look really cool. They could be built like plains biomes with custom savanna-style trees, but the actual biome could be desert in order to give them the look of a relatively hot, dry environment.
