It's Java and Python that have lowered Perl in use, not perl6.
Python has no doubt eaten into some of the space that was Perl's. They are quite similar in many respects and the choice of which to choose for a project will have little to do with the technology and more to do with available code and the programming team's preferences.
But Java? Nah, I don't buy it. Java and Perl are about as far apart as you can get in terms of both language and implementation. Pick any project and you won't find anyone hovering between doing it in Java or in Perl - the spec will dictate the language every time if that's the binary choice.
Secondly, Perl6 hasn't lowered Perl usage yet. But it will, and not from a technological standpoint because Perl6 will always suffer from the same implementation problems as Java due to its architecture. No, it will have a detrimental impact on Perl usage purely because of its name.
My anonymous brother jested above about Perl7. If there ever is to be such a beast I hope that TPTB learn their lesson from the Perl6 naming disaster and choose to call their new language something else entirely. Python4 would be an amusing name for it.