In contrast, with Python, on a weekly basis I run into 2.x and 3.x problems...last week it was running the Google Cloud SDK, which is 2.x only. I say this as someone who has almost switched exclusively to Python (3.x) and enjoy it...but man I miss the days of Ruby's ease-of-use.
(but yeah, 1.8 to 1.9 was not a lot of fun, but thankfully, many years have passed since then)
This is the same issue facing Perl (although the Perl situation seems more dire) WRT Perl 5 vs Perl 6. For Python maybe the benefits of keeping Python 2 alive for large users offsets the harm of any confusion, I have small projects (all in Python 3) so it's a rare annoyance rather than a deal breaker.
The situation with Perl is neither more dire nor really the same issue as with Python. Perl 5 is not going away. Perl 6 maintainers are not the same people as Perl 5 Porters -- both will be maintained for the foreseeable future.
Second, Perl 6 is a significant change to Perl, with far more features and somewhat different syntax. People will want to change for the features. Running Perl 5 code from inside Perl 6 works by calling out to libperl, which runs a real version of Perl 5. Perl 5 will still be popular due to ubiquity, access to CPAN modules, and things like CPAN Testers.
So it's a choice for the developer, to develop in a new language that just happens to be Perl-flavored, or to go with any other language. Not really a crisis.