You have to bare in mind Perls roots are as an awk-like language for the command line. In those instances weird line noise syntax was the idiom and as Perl grew it moved away from that but without breaking compatibility by default.

This leads to serious Perl projects relying on the numerous headers (as described in the very article we are discussing) to ensure everyone applies a more modern coding style.

So you can absolutely stop people from using $|

The point of Perl 7 is to have sane defaults.