Of course, such an idea would never work...the forum would rapidly die.
Indefinite probation with permanently reduced privileges and pre-moderation would only be applied to the likes of you Mr. QAATT. There are only two or three more like you who would need this condition applied to them.
It would completely knock the wind out of your sails once and for good. You know this and it terrifies you. But you and your cohorts brought us all to this point and something needs to be done about you.
The forum wouldn't die. You and your fellow trolls have frequently been suspended and even for years and yet PF has still been going strong with or without you.
As I had to remind one of your cohorts the other day, we are all only registered guests here. Others are free to post whatever they want based on relevancy to Poland and moderation. Their posts may prove to be extremely popular and they certainly don't need you here to weigh in and give your consent.
Reduced privileges and pre-moderation would still allow you to continue to participate (for whatever that's worth) while curbing and mitigating the negative effects you have on the forum when you predictably relapse into antisocial behavior. It would also assist Admin and the Mods upfront by allowing them to prevent fires from starting in the first place rather than having to exert time, energy, and patience extinguishing a conflagration after it started.