drywall VS OSB
You didn't say why you don't want to drywall. Is it because you can't 'nail' the trim to the drywall (vs. being able to do so w/OSB up there?) Is it because you don't like the look???
Personally, I don't think it will look that nice. A ceiling with 'lines' running across it makes the room look smaller and too symetrical. (It's a personal opinion but it is your house.) I don't see why you can't glue the trim up there on top of drywall instead. Personally, I think it will look nicer.
My best to ya and hope this helps.
Jay J -Moderator
PS: God Bless America!