I'm not so sure about your straw man. Yes, we know that Perl 6 is very different to Perl 5. But, to many people (dare I suggest most), it's likely that Perl is Perl is Perl. They will understand things like "not a new enough version", but not the arcane messages (like I posted above).

Look at it the other way around: if there is a way to make Perl 6 scripts fail under Perl 5 with an error saying "This is Perl 6 code, but you're running Perl 5", surely that is the best way to have it? After all, if you mix your Perl binaries in 5.x, judicious use of 'require' means that you're not going to get "spewed" as often as you could do, and when it happens you know why.