I see it requested a lot and I have a problem with that line of thinking.Having all infantry UU's effected by supplies would be a good change, IMO.
Supplies exists just to increase to price of entry of the swordsman line. Militia/maa would be OP if they cost 45f from the start, so their food cost stays high in the early game and you can get supplies to make them relevant later on.
There is no such concern about infantry unique units. They are not too strong strong from the get go, so there is no sense in adding an extra tech to be able to properly train them.
If some infantry UUs are deemed too expensive, then they simply should have their cost reduced. Adding supplies for them is needlessly making it more expensive to tech into them, and it doesn't make sense from a design perspective.