Devel::Declare is a module, Perl 6 is a new language which wishes to co exist with Perl 5. Whereas Python 3 wishes to REPLACE Python 2. Unfortunately with Python that's not an option. Not that its surprising. Python's syntax is rigid enough, any thing that is even close to changing/modifying/updating or getting a better syntax will break Python's back ward's compatibility.

If your only goal is 'readability matters', you shouldn't be surprised when programs get difficult to write over time.