It seems "disturbing" is the good word here, as the kind of changes in the semantics or notation between Perl 5 and Perl 6 almost guarantees that most potential users would have to decide if they are going to reject using one or another: The need to "read differently" on the distant look similar code demands too much from the people who'd just like to "get the job done."

What's that $1? Well it's the first match if it's Perl 5 but it's a second match if it's Perl 6. But don't worry, the other things in expressions also have sometimes other meanings.