I actually did notice that about the Shikai. If he doesn't have access to Zangetsu's power anymore, his Katana should have dropped all the way back down to the way it was in the beginning of the series.
Quote Originally Posted by November 11
In short,

Current Vaizard = Shinigami (zanpaktou) + Normal Hollow

Next level is

Dual wielding Vaizard = Shinigami (zanpaktou) + Arrancar (Hollow Blade)
Yep, that's my theory. Either that, or the Zanpaktou and the Hollow sword are merged into a single new weapon.