It would create no further confusion than the current system of letting a newly built jackson happily blast away at a Pzgren blob.
If nothing else AT guns should have this added for quality of life.
A jackson not hitting infantry has the same learning curve as learning that SMG troops only do dmg up close - i.e. you learn it after 1 game.
A new player can look at his screen and instantly see which units are only on attack vehicle mode without having to identify the units themselves.
If they want to dive a dive an IS2, they don't have to make sure their P4 has the symbol, and the panther that they have been using to kill some shocks doesn't have the symbol for some reason.
Conversely, if they want to A-move across the map as new players tend to do, they just have to make sure no units have the symbol so they don't run headlong into enemy infantry.