Thanks for your time. I suggest you (or somebody else) to officially reject PEP 580.
I start working on reformulating PEP 590, adding some elements from PEP 580. At the same time, I work on the implementation of PEP 590. I want to implement Mark's idea of having a separate wrapper for each old-style calling convention.
In the mean time, we can continue the discussion about the details, for example whether to store the flags inside the instance (I don't have an answer for that right now, I'll need to think about it).
Petr, did you discuss with the Steering Council? It would be good to have some kind of pre-approval that PEP 590 and its implementation will be accepted. I want to work on PEP 590, but I'm not the right person to "defend" it (I know that it's worse in some ways than PEP 580).