I imagine that given/when will be kept. However, the perception is that their current implementation is highly flawed. A new implementation will probably break some existing uses of given/when, so it makes sense to start warning people about this.

given originally used the lexical $_ rather than the global $_ (but this has changed in 5.18). This was confusing for many people.

when adds a whole extra layer of weird.

Quick quiz! What does this output?

use v5.10;
use strict;
no warnings;

sub two () { 2 }
sub three  { 3 }

sub english_number {
    my $number = shift;
    given ($number) {
        when ( 1 )      { return 'one' }
        when ( two )    { return 'two' }
        when ( three )  { return 'three' }
        when ( 4 )      { return 'four' }
        default         { return 'more' }
    }
}

say english_number($_) for 1..5;
[download]