Maybe yet another layer of abstraction might make it even nicer:

package Array::Extract;

my $worker_pkg;
my $priority = -1;

sub import {
    my ($class, %args) = @_;

    if (exists $args{priority}) {
        # Register new implementation

        if ($args{priority} > $priority) {
            $worker_pkg = caller;
            $priority = $args{priority};
        }

    } else {
        warn "Using $worker_pkg, priority $priority\n";
        $class->SUPER::import(ARRAY => $worker_pkg);
    }
}

# Worker.pm
package Array::Extract::Worker;
use Array::Extract priority => 1;

# somewhere else
use Array::Extract::Worker; # has to be used first
use Array::Extract;
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This avoids these global variables that have been described as "action at a distance". Using "priority", you can even have several implementations, and it will choose the one with the highest priority; but that's just an extra bonus, it'll work without priorities too.