There was no Perl 5 to Perl 6 migration. Perl 6 was announced, a bunch of design work happened on it, and then it became a different language run by different people rather than a version of Perl. People are still writing Perl code extensively, and Perl 5 is still maintained.
I would expect Python to follow a similar language split. People were disappointed at how few breaking changes occurred in 2->3. If there was going to be a 3->4 migration, will be a large number of proposals to correct other deficiencies in the language.
