if started as an interactive session python should check for and read ~/.pythonrc.py by default.

furthermore there should be two options added:
--rcfile filename
this will read filename instead of ~/.pythonrc
--norc
this will prevent reading ~/.pythonrc

(this is inspired by how bash handles initialization)

afterwards the variable PYTHONSTARTUP can be deprecated.

as far as i know, everything which can be done by the variable PYTHONSTARTUP can be done with the suggested method. the advantage of the suggested method is that it is "intuitive" in the sense that it is the way most other tools do it (bash for example).