Yo...I really doubt that Yamamato Taicho would show up...
The only time I think that he would EVER use Bankai on Ryujinjakka (his sword) would be to protect the King in the other realm, which requires access by a certain key (read the manga several chapters back for info).
As for the Kenpachi sword release, we'll have to wait and see.
And yes among the "OH SHIT GOTEI 13 IS HERE!!" approach, just remember who faced/fought whichever Shinigami Captain in Soul Society and match accordingly in terms of rescue, with exception to Rukia of course (Byakuya and his damn scarf).
Hitsugaya was used wayyy too much by the way...Aizen treachery in Soul Society, Arankar Invasion, and Bleach Movie. I'd rather much see Tatsuki and friends evolve into something more...or at least flesh out the Quincy Cross history a bit. What were there, like three total in the entire series until Ishida's grandpa was carved up (Not gonna count the Bounto story arc /fail)?
End Game Prediction for Hogyouku story arc in Hueco Mundo:
Ichigo vs. Aizen (duh)
(with Ichigo's inner hollow fighting instead, and possibly some new attacks other than Getsuga Tenshou, and maybe a release higher than Bankai [not likely])