pip team said they won't support setting limit for major version
of package being installed in the way below until it is supported
by PEP 440.
I think that's misrepresenting them. They explained why it isn't needed, and threw in an "anyway, it's not up to us"; they didn't say "sounds like a good idea, but you have to fix the PEP first".
Also, if you can't use pip 6.0 or later to take advantage of the already-working syntax that they recommended you use, how would you be able to use your new syntax even if it did get added?
pip install patch==1.x
The current way ==1.* conflicts with system shell expansion
and the other way is not known / not intuitive.