Valve already implemented that in Dota 2 with a hidden tier where game ruiners, bot users/exploiters, etc would be grouped together. They also capped the max EL

Valve already implemented that in Dota 2 with a hidden tier where game ruiners, bot users/exploiters, etc would be grouped together. They also capped the max ELO you could gain during calibration if you are in that shadowbanned tier. It was calculated based on the number of reports you received in the last n games.