Well. I'm getting a big indication that Unicode is a priority, moreso than back compat. This has got my head buzzing with ideas... such as detecting old Perls and conditionally enabling Unicode if the Perl is new enough. I just don't know if it can be done at runtime -- haven't tried it yet. Seems like an unwise strategy.
I may just throw down the guantlet and support Unicode, requiring 5.8 from now on... after all, that's what Perl did. If you don't like it, you can always go get an older version, right?
A mistake can be valuable or costly, depending on how faithfully you pursue correction