I'd say the amount of actions against you would probably border on getting permabanned. or have some sort of review available. Honestly is it any different than it is now with people saying that certain NN's are "out to get them"?
The whole point of being a mentor is just being available. Would any large group of people be that petty about not letting someone try to help? ... well yes... but any more than they can now?
I think the removal of any rewards or exclusivity would take away any sort of "prestige" people linked with it and you'd be more of an info booth sort of presence than being special.