Just saying, this thread will most likely be locked because any talk of bans, whether just ideas or not, are usually prohibited but I dunno.
But I'll still throw my two cents in. I know for a fact that when a banned member tries logging in it'll tell them how long they are banned for. Reasoning...not so much. Although most of the time when the player is in game and gets kicked from there, they'll have a kick message and the reason more often than not. So in all reality, this is already in place. ^^ Hope this helps.