Now it looks to me like an overhead without any real gain.
As far as I know from the few hours I helped with the port, the slots automatically update the opposite relationships. So if you add an attribute to a class, the attribute will automatically point back to the owning class. The same same happens if you set the owning class of an attribute to a different class all the relationships are automatically updated.
The few times I used the "old" Moose I found it quite annoying and error prone that I had to manage all these opposite relationships manually. I think this is a big advantage, if I observed all this correctly. I might well be wrong ...
Lukas