Are deprecated special variables (like $# and $*) lost forever or would it be possible the reuse them in a future Perl version?
There's no reason why they couldn't be reused if an appropriate use 5.16 or some such is present, but that would be terribly unlikely. Firstly because it's just asking for trouble (it will confuse the hell out of people), secondly because special variables are a nasty thing anyway and introducing a new one is rarely a good idea. You can probably consider them lost forever.