Personally, I see this looks a poor solution; admins/mods would get thousands of posts to verify, on top of their already existing workload.
That's the reason why such a feature won't ever be implemented. I've seen forums that do exactly what OP is suggesting, but they have far fewer members to deal with. I forget the figure, but bitcointalk has multiple millions of registered users with thousands of new ones registering every month. There's no way in hell mods would be able to approve posts.
Newbie jail was a reality when I joined. I think it should absolutely definitely make a comeback.
I wasn't around for that, but I've certainly heard about it. And while I agree with you that it really ought to be brought back, I do believe I've read that Theymos isn't even considering it. That's unfortunate, IMO.