I agree with the mods that the OP’s suggestion is not a good match for the SDMB. However, I do think restricted forum posting is a very useful tool that could be used to improve rule enforcement. For one, it would allow mods to create consequences for behavior that is occasionally annoying without really being deserving of lifetime banishment. Getting too feisty in GD, posting too many trivial threads in GQ, threadshitting in CS: people might think a lot more carefully about stuff like that if they couldn’t post in those forums for a day/week/month. (Trolls and spammers you still just ban as always.)
I think it would be interesting to create a usergroup that only has posting access in ATMB and The Pit. Use the infraction system to create shortcuts to move people into that usergroup for short, fixed amounts of time (e.g. 1 hour, 8 hours, 1 day, 1 week, 1 month). Give individual mods full discretion over the 1-24 hour options, get some consensus for the longer ones. There would then exist a middle ground between “no, really, please stop it, I’m serious this time!” and “begone FOREVER!”
The mods would be able to control their forums in a more nuanced way, and the board would lose less otherwise-excellent posters like Diogenes simply because he racked up too many ticky-tack fouls. I think it would be win-win.