As it stands, enumerate() already takes a "sequence" keyword as an
alternative to the first positional argument (although this seems to be
completely undocumented). So, as you say, METH_O is a no go.

I agree with you in that my original complaint with the positional
argument was that enumerate(iterable, start) was "backwards." My other
argument was that a large number of these iterator utility functions are
foo(*iterable) and upon seeing enumerate(foo, bar), a reader might be
inclined to assume it was equivalent to enumerate(chain(foo, bar)).