perl 6/raku was a redesign. as far as i remember, upgradeability from perl 5 without code changes was never the goal.
We thought that it would take a year or two, not decades.
Also, the intent was to have a Perl 5 compatibility mode.
Maybe not the one that was originally planned. But that was only a real possibility if Perl 5 would be able to get rid of its XS addiction.
Ask yourself: how many of the up river Perl modules are Perl only?
Perl 5 is still supported, Perl 6 (Raku) continues independently.