My $0.02 is you'd mostly want to learn Perl6 if you were after something like Ruby but perhaps with more room to express yourself and form a community and build new technologies. At least I really love the language and find it very expressive and intuitive to use and it has a lot of features useful for doing Bioinformatics built in (something I'm going to add to the P6 advent calendar on the 15th Dec). The extra level of detail ten years of design puts into a language like all the funky features working together and being consistent helps a lot. So much of the cooler expressive/functional stuff in Python feels out of place like lambda and list comprehensions. Maybe I'm wrong but I wouldn't write anything /that/ complicated or important using Python lambda or list comprehensions. They just don't play that well with the surrounding code you will have to write in a different style. I can't attest to Ruby since I don't know it well. I felt it was quite close to Perl and I'd be better placed learning Python instead, especially for a job writing code that wasn't for the web.
Maintainability, productivity, etc. of Perl 5 is on the same level with Ruby. And I don't think Perl 6 improves on that, so it's probably the same too.
Personally I don't see any benefit for anyone to switch between mentioned languages. They all have similar problems.
Those sorts of answers from other's perspectives is what i'm interested in for Perl6 (not 5) over ruby. I think I know many reasons to prefer perl5 over ruby (although I don't), but once you leave perl5 for perl6... I'm not sure why you wouldn't just ruby (or python). But could be just cause you're used to Perl and like Perl. Or could be because there's something about Perl6 you especially like over ruby/python. Etc. I think it's a reasonable question?