I wonder if part of the problem here isn't that protocols are primarily focused on instances, where the __init__ method is explicitly *not* considered part of the type.

IIRC supporting protocols for classes was an afterthought.

That said you have made a good case for seeing it as part of the protocol  when the Type[] operator is applied to the protocol.

So yes, I think we should be careful ruling that out too soon. Do we have any evidence that users are confused and define __init__ methods on protocols that are being ignored by their type checkers? The OP didn't say.

When in doubt, let the status quo win.