ae78ae4 merged the removal of smartmatch, which was planned for Perl v5.42.

After more discussion, the PSC believes it would be better to make the removal guarded by a feature.
(Similar to what was done with the indirect, multidimensional, bareword_filehandles and apostrophe_as_package_separator features.)

That feature would be included in the :default feature bundle and all bundles up to :5.40. It wouldn't be included in :5.42. The main benefit would be that none of the unmaintained modules on CPAN and elsewhere would break, while newer code (declaring the Perl version it codes against with use VERSION) would not be able to use smartmatch any more.

The proposed name for the feature is simply smartmatch.

Note: This goes against the idea proposed by @iabyn of creating an "air gap" of multiple versions without a smartmatch, that could allow to re-introduce a better smartmatch in the future. It is still possible to take this approach in an undetermined future.