Revoking invites was possible before recent tournament changes - and i think it would be good to have it back. But even then you weren't able to remove someone who already joined.
I don't think it would be good to give host so big powers. People don't check tourneys every day and you can easily imagine situation that tournament starts and you notice, that you are not in the team you expected to be - just because host moved you.
I've already described solution to your problem (allowing only full teams to join team tournament https://www.warlight.net/Forum/83352-coin-tournaments?Offset=56),i
would create uservice, but i'm too lazy and don't really believe in it's importance :P