I suggest we use newbie convention and call it Perl (watch the case!), so we could say "you need to use Perl not perl to parse Perl 6 Perl, because you use perl to parse Perl 5 Perl, PERL is reserved for Perl 7". That would be funny, especially for Windows users.

Nah, seriously, I like your idea best. This is what python does between 2.2 and 2.3 and it seems to work for them. Unambigious, and dead-on straight forward. Plus, it means the interpreter/VM can be a little cleaner for not understanding compatibility. This doesn't mean the perl6 executable couldn't detect the lack of a module/class and option out to perl5 via exec...