There's allways room, I would think.
If there is a limit, we should have it around 20 or so if its needed. More then that, and we would prolly have to add other special roles to balance it up (Lawyer can save two times a game someone from being lynched, jailer jails someone so he cant vote or post in the thread a whole day, corrupt cop being a gangster who gets to know who the detective is investigated, not who the detective is, etc). But so far, no need, and it would perhaps complicate things for rookies playing it for the first time.