I think this will work out ok if .meta.can, when it's looking for wildcarding classes, distinguishes classes that define their own .can from those that don't,
and only adds autoloaders to the end of the list that aren't shielded by a corresponding .can method. (The problems Perl 5 has with defining a .can method
in a class shouldn't arise in Perl 6, which tries to prefer "next" semantics to "super" semantics. At worst we'll
require people to say "next METHOD" at the end of each such .can method definition.)
If I make a few assumptions about how .meta.can works, that should work out. (As long as you're aware of the issue and want it to work out, I'm sure that you can fulfill some set of conditions to make things work out.)
I'm guessing that the programmer would still need to synchronize .can and AUTOLOAD in some way, but a mechanism to make that easy should be simple to add at the user level.