I'd rather they perfected 5, rather than start from scratch with 6. Chances are 6 wouldn't be better than BNW until after at least the first expansion. The easiest way for them to make me happy would be to release some more quality scenarios as DLC. A SMAF spin-off would be more work, but also make me very happy. I think it's safe to say I'll by anything firaxis releases for Civ 5, or X-Com, as long as it continues their recent quality level. BTW, if I'm interpreting the Steam DB history right, it seems they're working on a new patch in addition to "Bison."