User blog comment:StonerCatJay/Rereading the series- theories and speculation/@comment-4207271-20140522011541

I like the idea of Ichigo's Bankai not being a Bankai, it works and doesn't for these reasons I've come up with so far (Not counting what you've said):

Pros - During his final fight with Grimmjow he released it without a word, it just, happened.

Cons - Zangetsu used it in Ichigo's inner world. When Jugram broke his Bankai, it had to be reforged, whereas a spirit weapon would simply be re-formed.