I think a lot of people (or just me) misunderstood the "show me your bankai" statement. I think Kensei suspects Hisagi is capable of 'waking up' his Bankai and learning to use it, I don't think he just has one stored up. Nor do I think all the other lieutenants have it either, that would be just... thick.
The giant dog was a pretty sick looking thing. I do hope it doesn't mean YET ANOTHER fighter on the Soul Society's side though... I mean... well, it seems like the odds are just stacking right up against the Quincies. Sure, Juha Bach and his henchmen are pretty damned powerful. They can also take Bankais (unless you happen to be Ichigo). But now we've got the 13 Divisions + 0 Division (apparently stronger than everybody in the 13 combined) + Kukkaku, Ganju and the Fullbringers + Grimmjow, Urahara, Orihime and Chad + the Visoreds and Yoruichi, wherever they happen to be right now.
And a bunch of the Sternritter are already dead already, mostly thanks to Kenny and Yamamoto.