To be honest, I was surprised to find that it was still valid in v5.34 — thanks for the info.

I had written, "I haven't used [it] in over 20 years"; upon reflection, I believe my last usage was probably in 1996 or 1997; so that's closer to a quarter of a century.

The message, to which you linked, had "... $user's problem ...", followed by "This bites experts and new users alike ...". I suspect I could have been one of those bitten, if reviewing another's code without "use warnings;". In v5.28, a new warning was added: see "perl5280delta: New Warnings" and "perldiag: Old package separator used in string". My normal code would be something along these lines:

ken@titan ~/tmp
$ cat pm_11137628_pkg_sep_in_string.pl
use strict;
use warnings;

my $user = 'ken';

print "... $user's problem ...\n";
[download]

which, when run, gives me ample feedback:

ken@titan ~/tmp
$ perl -v

This is perl 5, version 34, subversion 0 (v5.34.0) built for cygwin-th
+read-multi
...

ken@titan ~/tmp
$ perl pm_11137628_pkg_sep_in_string.pl
Old package separator used in string at pm_11137628_pkg_sep_in_string.
+pl line 6.
        (Did you mean "$user\'s" instead?)
Name "user::s" used only once: possible typo at pm_11137628_pkg_sep_in
+_string.pl line 6.
Use of uninitialized value $user::s in concatenation (.) or string at 
+pm_11137628_pkg_sep_in_string.pl line 6.
...  problem ...
[download]

I don't have anything earlier than v5.30 on that system:

$ perlbrew list
 * perl-5.34.0
   perl-5.33.5
   perl-5.32.0
   perl-5.30.0
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However, on another OS:

C:\Users\ken\tmp>perl -v

This is perl 5, version 26, subversion 3 (v5.26.3) built for MSWin32-x
+64-multi-thread
...

C:\Users\ken\tmp>perl pm_11137628_pkg_sep_in_string.pl
Name "user::s" used only once: possible typo at pm_11137628_pkg_sep_in
+_string.pl line 6.
Use of uninitialized value $user::s in concatenation (.) or string at 
+pm_11137628_pkg_sep_in_string.pl line 6.
...  problem ...
[download]

Not quite as "ample" feedback. I expect I could work it out from here; others might be saying frustratedly: 'But there is no "user::s" in my code'.

I read through about the first dozen NNTP messages. Most discussion seemed to be about whether removal should be partial or complete, and backward-compatibility. When I got to https://www.nntp.perl.org/group/perl.perl5.porters/2021/08/msg261321.html and read "... disks of infinite size coming free with a packet of corn flakes ...", I had a chuckle and left it there. I wouldn't personally have any problem if the old style package separator was removed permanently and completely.