A normal use thing, like use strict. Yes, it would mean that you couldn't play some of the fancier tricks but, well, too bad, that's what you asked for when you used the pragma. :)

if I do it right, it won't stop imported subs, nor subs you declare but don't define, so you can AUTOLOAD later. You'll have to have a "sub foo;" somewhere, to make sure the foo sub's noted, but that's fine.

I expect this will end up tallying the subs that are used in the blocks that it's in force, then at CHECK time making sure there are entries in the GV slot of the appropriate symbol table entries, but as I said I've not nailed down exactly how it'll behave yet.