> I'm using it both for comparisons which needed to build an abstract base class and typing. Currently there are 2 ways, i need to create a dummy abc and put type() calls everywhere or i need to set a constant to my module and _abc_data is totally irrelevant with this. I dont think users want that.

It doesn't make sense to me.  Could you elaborate?


> Abstract base classes can be called a core part of python too

abc is core part.  But note that _py_abc can be used instead of _abc.
_abc_data is used only when _abc is used as backend of abc.
At least, your pull request doesn't work correctly when _py_abc is used.


>  and when someone needs to obtain type of the struct that holds state of ABCs it shouldnt be hard, types module should expose it.

I think it is bad idea and we don't support such usage officially at all.
Such code doesn't work when _py_abc is used.