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You are right, I did not look deep enough. I was fooled by the conversion of NotImplemented, returned from object.__le__, etc, to TypeError. Sorry for that noise.
For comparison and arithmetic, the actual alternative to defining a function that returns NotImplemented seems to be to not define it at all.
class C():
 def __ge__(self, other):
 return True
 def __add__(self, other):
 return 44
 __radd__ = __add__
class O():
 pass # removed NotImplemented defs
 
c = C()
o = O()
print(c >= o, o <= c)
# True True
print(c + o, o + c)
# 44 44
(I looked at the codes for binary_op1 in abstract.c and do_richcompare in object.c and do not yet see any effective difference between not defined and a NotImplemented return.)
I'll take a look at the patch later.