I'm sure if you are reading this, you know who "Godzilla" is (was :-) ) on comp.lang.perl.misc. She is constantly ( sometimes rightly) bashing perl5 code, saying perl4 style code was faster and "good enough" for some purpose.
So I prognosticate many Godzilla-style dinosaurs, some who are very respected Perl programmers, who will just keep on claiming that Perl6 is a waste, and Perl5 will do it just fine.
I also see this common scenario: A question will be asked, the standard Perl5 answers will appear, but someone will point out how much easier it can be done in Perl6, OR if it was done in Perl6, it will avoid some sort of hidden problem. Then eventually, more and more people will start using it.
I also forecast that a bunch of people will want to use Perl6 to make binaries for distribution, to hide their source code, and all the pro-con discussion which goes with that. (It seems that most new programmers want to hide their code :-) ).
Finally, I see a flood of new Perl6 books, and Perl5 books going for $1 or $2 on ebay. People will be discussing whether it is worthwhile to read the old books.
I base my forecasts on my observations of human behavior, not on the merits of Perl5 or Perl6.
I'm not really a human, but I play one on earth. flash japh