Right, and you could do all that on a BX board. You don't <i>need</i> a full freestyle shape to do any of that. (and all freeride boards are basically a full frestyle shape - just different construction)
Right, swing weight doesn't matter <i>as</i> much to carvers, but that wasn't my point...
Yes, but also freeriders - people who want to both carve and not carve, in softboots. A shorter board with low swing weight is more important to them in the trees and bumps and just for general maneuverability. But if they could have an extra 5cm of edge length with a BX board of the same overall length, it would carve better and handle more speed.
That's why I believe most softbooters who mostly just cruise the mountain should really be on BX boards.
As for why race boards have square tails, well, it's just about maximizing edge length for more speed and edge hold. Race/freecarve board tails are usually 5cm worth of non-running length. Race/fc board noses are usually 15cm. You could make a twin tip race board, but it would be 10cm longer for no real reason. I'd rather ride a 170 than a 180 if the 180 isn't going to be any faster or more stable than the 170.
Like I said, having a twin tipped board is only <i>necessary</i> for logging lots of time riding fakie and for launching/landing big airs switch. For casual fakie antics, a BX style tail is plenty. And behold and lo, that's what is on the all-mtn carvers like the Axis and 4x4, etc.