Here's a quick intro to supplies: http://perl6advent.wordpress.com/2013/12/19/perl-6-supplies-...
Here's a more in depth exploration of Perl 6's concurrency features: http://jnthn.net/papers/2014-nlpw-reactive.pdf
If you want to use a dynamic language (albeit also offering optional static typing) with powerful concurrency options that doesn't also involve s-expressions, I think P6 might be one of the few options available. I'm not familiar with Ruby, but from what I've heard the default runtime has some limitations when it comes to concurrency, and while it's been a while since I used Python, I recall hearing that it also has some problems with handling concurrency.
The short answer, is that the comparison isn't fair to either communities. Perl 6 has many killer features. Concurrency, Macros, Grammars, Regex goodness, functional programming features, OO features, Strong typing support, user defined operators, multiple VM backends, Continuations to name a few. But there are many many others.
Perhaps the most killer feature of Perl 6 is like lisp, you can use the language to grow itself without breaking backwards compatibility. This alone will ensure that the community can grow without worrying about breakage, regression and backwards compatibility.
Read more here: http://perlcabal.org/syn/
Ruby and Perl 5 definitely have more libraries, users and a far more mature ecosystem of things. But I guess the sheer awesomeness of Perl 6 will attract a lot of developers and that will have a healthy community of its own.
In short I think there are plenty of reason why one would chose Perl 6 above Ruby.
I don't know if it will be the same for perl6, but at least with perl5, backwards compatibility was rarely broken. Every time my debian-testing box upgraded a ruby version, it broke something. From 1.8,1.9,2.0, and I think 2.1 actually worked without any issues...
This is never an issue with perl5. And before you say "perl is dead it never changes", go look on the perl5porters mailing list. There are a ton of changes going on. I had every intent this year to join the dev team, but the commits come in so quick on that mailing list, I can never find a place to start. When perl5 updates to a new version (which has been happening once a year for like 5 years now), it is not just a few bugs that are fixed, but a whole lot of new features are added and plenty of new syntax to scare the heck out of anyone. So an argument of the ruby dev cycle is 'slower' probably won't hold up.
Onto more perl6 specifics, I think one of the original goals was perl6 being able to compile a script into a raw binary. Don't know if that feature will be implemented. Ruby can't do that, though it does have the JIT compile stuff. So I guess that could be one reason..
Perl6 is new, so I guess it is full of new "technology and stuff" right?
I personally never did much with ruby. I tried to use it as my first language to learn with. I signed up on some hacker forum wanting to learn to hack with my new found ruby skills... They just booted me with the message of "ruby aint really programming". This was back in 2007, but I never could get over that...
From then on I only used Ruby when I couldn't figure out how to do something in perl. So none of my ruby scripts have ever been seen by another pair of eyes. I keep them all hidden, knowing that they are cool and all in their own right, but knowing if I were just a little smarter... I could have written it in perl...
Wait, what? There are are specific use cases where this might still be true, but as a general rule, this hasn't been the case for some years now.
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?
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.
Why would you use Perl6 instead of ruby?