I would not want that to happend. Not that i have anything against japanese art style, but it just won't suit Halo.
You see where Halo wars went, and i did not like that at all either(Talking cut-scenes).
(Not that it went bad, i just didn't like it.)
It was ok with the Halo legends(even though i hate it.), but if H4LO is going to turn out like what the trailer looked like, "me no liek it".
So i hope it was just to get a trailer for E3 and that is does not stay that way. This is all just my opinion though.