It doesn't matter if the package is empty, a STASH was created to hold the symbols.

And the initial overhead for a hash is profound, even if it's empty. Like I said several hundreds of bytes.

Furthermore do I remember someone explaining that packages which become classes receive further optimization. In order to speed up method lookup (IIRC), but I don't really know the details..

I'm not aware of any application which tries to generate a massive amount of pseudo packages, I'm just saying it might not be the best idea to create many global data structures which are never destroyed.

And if you only generate a small number, take care about controlling the namespace, because they are global.

Fun fact: As a side effect of my experiments I was even able to block a package name in a way that any further package blocked_name; would globally fail.

Like: "Hey I hate Moose, if you use my module in your project you won't be able to ever use Moose later!" ;-)