Would it be possible to unconfirm people when they get blocked (possibly as an extra option for admins on the block page)?
Not at the present. You could file a feature request at bugs.wikimedia.org. But it doesn't seem terribly useful to me (you have to simmer for four days before making trouble again?).
The reason I suggest it is because the reason most people give for an edit count requirement is that once you've reached X edits, we'll know if you're a vandal or not. However, us knowing isn't much good if you get autoconfirmed anyway. Unless we want to indef block all registered vandals as their first block, an edit count is useless without it being possible to prevent autoconfirming if the edits aren't acceptable ones.