I think it's absolutely fine for a bunny to have their own room, except for exactly what was mentioned before- they need to have their own smaller space to hide away in if they want it.
As long as the room is safe, no places for him to get stuck or basically anything in there like a cabinet or a table etc. and obviously no cables or electricals then why not? What a lovely big space he will have.
I would also say that although that's really nice for the room, it might make the bun maybe not get as much socialisation? The door will be closed even when you are there and you'd have to make the conscious effort to go in there, whereas if he was in the living room or your bedroom etc. there would be a lot of contact even when you weren't specifically spending time with him. ?
Benji has a 5ftx2ft cage that's permanently attached to a medium-sized dog NIC pen. And when I'm here he is out with me- I obviously watch him but there are pretty much no hazards, except a few cables behind the tv which i keep him away from, and obviously table legs etc. but he never pays attention to them.
Jen