Perl 6 is no joke. For many years (2005-2015), I thought it would end up as vapourware or at least unimplementable, so I stopped following the project. But suddenly (or so it feels), there's a working compiler and one or two virtual machines that actually work. The language specification and the implementation are converging. Inline::Perl5 is genuinely cool and useful, even if neither it nor the compiler are "production quality". Now I feel the project will eventually succeed, even if it takes another 5-10 years to a full, optimised, mature implementation.
When it comes to books about Perl 6, the biggest difference to Perl 5 is that you can write a book based on the specification and it will remain valid and up to date for many years, even if the implementation changes. You can hardly say the same of Perl 5, which only has one implementation and no specification. I look forward to reading more Perl 6 books. I can't recommend it for production use at work, and I likely won't use it much in the next five years, but it contains so much that is new, interesting and Perl that I'll eventually make the switch. Just not yet.