i'm not sure if i understand what i'm talking about (so please correct me if i'm wrong!), but... in Perl 6 you could change the grammar, so you can get (at least syntax-level) compatibility with older versions, like Perl 5 or even Perl 4.

From What’s new in Perl 6 (The short form) by Dan Sugalski (the link points to a Microsoft Powerpoint file; there is also a HTML version in the Google cache):

• Perl 6 grammar is really a perl 6 grammar
• That means you can change it if you want
• Don’t like . for deref? Change it

so if i'm not dreaming, you could distribute your application with the grammar for the version of Perl that you've developed against, so you don't have to worry about on what perl version your code will run, because your application will load the correct language version from by you specified grammar file.

i hope this makes some sense :)