And since this Pipfile is just a bunch of function calls, why can't it just be put in setup.py? Or is the idea to eventually get rid of setup.py?
That hasn't been settled yet. It's being actively discussed [0].
> Or is the idea to eventually get rid of setup.py?
Yes, a replacement for setup.py has already been agreed on in PEP 518 [1]. It's called pyproject.toml.
https://pypi.python.org/pypi/flit
Looks quite nice, a flat .ini file for specifying deps, though it only builds wheels.