Thanks for writing such hard PEP.
At first glance, it new type hierarchy seems OK. But I can't understand rational for new flags.
And it's very difficult to estimate runtime and maintenance cost of the PEP, without draft implementation.
FASTCALL is introduced in recently version, and it make implementation complicated. I'm afraid that this PEP make it worse.
For making FASTCALL stable & public, I'm +1 if Victor and Serhiy agree.