I have no use for this either, and agree with rejecting it - in nearly 30 years, nobody has asked for this before, and it's still the case that we don't have an actual programming use case (some theoretical use in an abstract mathematical model isn't a programming use case).  Seems far more likely that someone applying floor() or ceil() to a complex number is confused.

math.tau was essentially useless too, but Guido wanted to add it mostly as a light-hearted inside joke:

https://bugs.python.org/issue12345

Against that, I see that the popular mpmath Python package does support it (for floor and ceil).  Perhaps you could get mpmath's author to chime in here with a "good" argument for adding it to the core language?

http://mpmath.org/doc/current/general.html#floor

"""
The floor function is defined for complex numbers and acts on the real and imaginary parts separately:

>>> floor(3.25+4.75j)
mpc(real='3.0', imag='4.0')
"""