Perl6 isn't done yet. Hard to document a very quickly moving target.

Hard, yes, certainly. But not quite impossible.

The fun thing about Perl 6 in its current form is that almost all changes are in syntax and things that Perl 5 didn't support. And even when a major Perl 6 feature is changed somewhat, the underlying principles are practically set in stone and stay the same. It's "just" the details that people work out now.

Certainly a migration book can already be written, as it is already know how Perl 5 things will behave in Perl 6. Well, except for very minor things like the flipflop. But for that, you can leave in a stub. It's not a show stopper.

When Perl 6 is in beta, re-read the book(s) and update everything to current. Run the test suite for the example code, and repeat that until everything passes again.

Perl 6 is a moving target, but that doesn't stop the Pugs team from maintaining more than 8000 unit tests, lots of documentation and of course the Pugs code base. And it shouldn't stop anyone from writing a book.

If you're not up to it, don't worry. Other people are, and the books will be there by the time Perl 6.0.0 is set free. Some even long before.