chromatic pointed out:

Perl 5 already has major version number increases, such as from 5.12 to 5.14.

Yes, I can see that, but perl5.14 will run almost any program that perl5.12 ran for you, and you probably appreciate this.

Now suppose, for example, p5p decided it was prudent to deprecate method-name package-name calling syntax. This would mean removing a feature, at least after a transition period with deprecation warnings. The warnings alone would hurt a lot of users of legacy code, who would have expected perl5.(n+2) to be largely consistent with perl5.n. Since p5p tend to be helpful people, they would hesitate to act like that.

Now if there was an opportunity to switch to a greater integer version number of Perl, there should be much more freedom in design decisions, since it seems reasonable to expect more substantial changes with more substantial version number increases.

I would like Perl to benefit from that kind of freedom. I understand that initially this notion was part of what started Perl 6. Of course there would be debate about what exactly would have to go into the new version of the language previously known as Perl 5, but I am sure we could end up with something quite practical.

... since it seems reasonable to expect more substantial changes with more substantial version number increases.

That seems reasonable to you. The same number means different things to different people. Certainly you know that Perl 5.15 is a development version, but tell a thousand Perl 5 programmers who aren't tied into PerlMonks or perl.org or IRC or YAPC or Perl Mongers that Perl 5.15.2 is out and see how many of them say "Cool, how can I get it?"

Perl 5 already had a version number change between 5.005 and 5.6.0. That change meant exactly what the documentation for the version number said it meant. The same would go for any other change.

The notion of perpetual forward compatibility (where use 5.12.0 means "Anything 5.12 or newer obviously must work!") has its obvious flaws. Fix that—that's one of the real problems, after all—and a lot of the handwringing over the meaning of version numbers can go away.

Perl is supposed to get a mechanism for that through use v5.099 - see Back to the __future__.

This is basically orthogonal to eliminating the "5" from "Perl 5" and moving straight to "Perl 16.0" next year.