run 100% of existing applications and all CPAN modules without modification. There are billions of source-code lines out there in production service, which must continue to run. The travesty known as "Perl 6" ignored that, and so it was ignored. Most of "the Perl language" is actually not the compiler, but the CPAN library. If you break
of that, your "new language" will also go nowhere, because it will be too expensive to consider adopting it.