1. Someone who hasn't actually played BNW isn't qualified to criticize the current state of the game. The changes resulted in huge game play differences in the middle to late game.
2. Before BNW "tall" 3 city play was boring in the later game. After BNW it isn't boring anymore, there's still so much more to do. One of the triumphs of BNW is it expanded to avenues of conflict beyond military warfare.
3. Domination victories w/ wide empires are still very much doable in BNW.
4. I disliked unit stacks in IV. I really like 1UPT in V. I'd be very disappointed if we went back to stacks. Hexes are also good because you don't have to keep track of how many diagonal moves you make (1st diagonal was 1 tile, 2nd was 2 tiles, 3rd was 1, etc. with squares).
5. I don't think I've seen Civ V use more than 1.5GB of memory. I believe the addressable limit for a 32-bit program is 3.5GB. What would we gain by making Civ 64 bit, other than slightly faster processing (there is a bit of a performance hit running 32bit programs on a 64bit OS).
6. Ok, so the AI could still be better, even though it has been massively improved since V's initial release. How will moving to VI magically fix that? It sounds like you're assuming that the AI issues are intrinsic to V's design and by doing a ground up re-write they'll magically go away. A complete re-design is just as likely to end up with AI like V vanilla.