This is a great way to confuse 99% of customers. It also violates the idea that all 4 ports are identical, and also poses a problem if the user has stuff in the other ports because now they need to swap multiple cables every time they want to change charge behavior.
Agreed it could be confusing without some sort of prompt. Or maybe it could be opt-in from the settings just like the iOS “Optimised Battery Charging” toggle.
Wrt all the ports being identical, it’s a bit of an edge case but there are already plenty of MacBook USB-C oddities. Instructions for monitors strictly plugged in on either side springs to mind as an example: https://support.apple.com/en-us/HT210754
