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This is a lot of work, for I think very advanced Composr usage. For most sites, Probation should be fine (already allows changing of privileges). Or just manually moving someone to another group. Maybe a feature whereby you could have multiple Probation groups, and you choose which, would be a reasonable middle-ground.
I wouldn't advise spending so much effort on making Composr do more and more, I think our effort should really on be making it more acceptable to a wider audience.

I'd think the ability to choose multiple probation groups would be even more complicated because of how implicit groups operate and how Composr gets / searches for the probation group.

I'm going to switch this to Sponsorship. It is likely something I'll need personally for a v11 site WIP which I'll develop myself and maybe offer as a non-bundled addon.