If you're about to introduce a change that only works on some version of Rakudo (or higher), there is no need to handle backwards compatibility in code. We're worry about that after christmas, orelse in post-beta state of Perl 6. Right now it's enough to tag the previous commit with the last Rakudo release that doesn't have what you need, and then we declare that users of such old version can use Panda no newer than the one with a matching tag.