Disclaimer: This post is entirely hypothetical. No decisions regarding Perl 5 have been made, or to my knowledge even been seriously discussed. It's entirely possible that Perl 5 will stay Perl 5 forever, or that the "5" will simply be dropped from the numbering (which would mean the next release of Perl is Perl 32), or something else happens.

Now that Perl 6 has been renamed to Raku, that theoretically leaves open the possibility of Perl 5 upgrading to Perl 7. I've thought about what features would warrant a major version number change, and that's what I'm writing about here. My list is probably not complete, and I might update it if I think of more.

First off, in my opinion, Perl should continue its tradition of being mostly backwards-compatible from release to release. If you want radical changes to the language, see Raku (and define your own slang) ;-)

• Subroutine signatures need to come out of experimental
• Smart matching should either be revamped, or removed entirely (Update: and if the latter, keep given as a topicalizer whose block can return a value)
• Various other experiments should come out of experimental - e.g. refaliasing and declared_refs are IMHO pretty useful.
• I'm not sure how this would be best implemented, but a "batteries included" Perl release would be nice. For example, one that includes Moo and other extremely common modules such as DBI. We might look to Strawberry Perl for an initial list.
• Update 2019-11-17: Implicit use utf8; and STDIN, STDOUT, etc. default to UTF-8 as well.

I imagine that, similar to Perl 6, a Perl 7 binary might be called perl7, with files being called .p7 or .pl7, .pm7, etc. Using this interpreter or this file extension would be the same as a use v7; (and turn on the corresponding feature bundle, etc.).

Again, these are just hypothetical and unfinished thoughts of mine :-)

Update: I accidentally created this post too early, sorry for all the additional edits. I'm done for now and further significant edits will be marked as such.