This is one reason writing code to support a feature is often more useful than writing a wishlist; code is less ambiguous than English.
I still do think that feature is the wrong approach. I'd rather see the burden of forwards compatibility placed on upgraders. What if we had a module which removed the new features added by default? If you're upgrading a large codebase, you can write use feature limit => 5.006; or something, rather than forcing all potential future code to enable new features explicitly.