Moo is very adept at providing a very lightweight and quick way to provide 'Modern' object oriented interface. While it is true that Moo itself has dependencies, I have observed that they are fairly lightweight.
Sometimes, the lack of certain features in itself is a feature, and I think Moo expresses this very well.
Of course, the lack of features.. is well.. a lack of features. But for what it's worth, I find dealing with Moo's "lack" of features easier than dealing with M[ou]ose's larger featureset.
Also, I personally find Moo's stack traces are easier to read and understand.
I wrote this module to test modules which I wrote myself because I was tired of writing boilerplate 'stub' code and all sorts of weird checks.
I suppose a future release can offer options to monkey-patch other (external) modules, but I'm guessing there's quite a few of those modules around.
I suppose it would be possible to make ->regstub accept fully qualified package names, and would allow the behavior you are talking about.
So maybe in a future release.