LanX presented this topic at the Frankfurt Perl Workshop last Sunday and we discussed it. The main point I find missing is, that the redefinitions can only affect code, and not data. This makes the whole thing a non-starter for me, since for example reloading a class/object package will only do what I want if I don't declare new accessors and don't restructure my existing object tree:

my $info = My::Config->new( Load( 'config.yaml' ));

# in My::Config
package My::Config 0.01 {
    use Moo 2;
    has 'include_files' => (
        is => 'lazy',
        default => sub { [] },
    );
};

# After update:
# in My::Config
package My::Config 0.01 {
    use Moo 2;
    has 'plugins' => (
        is => 'lazy',
        default => sub { [] },
    );
    has 'include_templates' => (
        is => 'lazy',
        default => sub { [] },
    );
};
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If the above happens, you will still have an object $info that looks like:

$info = {
    include_files => [],
};
[download]

... but the other code will never access the old data.

I can imagine cases where I want both, blowing away the old data, and keeping the old data, and I think there is no good "automatic" way of determining what I want in each case.

In limited situations, for example where programmer-users are allowed to rewrite some plugin code that gets hot-reloaded, and that plugin code is required to act in a functional way, that is, having no state of its own, reloading a module can still work.