You already can tell if a President is higher or lower than you are from his blip on the radar (▲ means he's higher, ■ means same altitude, ▼ means lower), but I can understand that it would be nice to know how much higher he is. However, it doesn't really mean anything until you know how high you are when you are near him on the map. Is he on a building? Is he parachuting? Is he on a high hill with a plane? I don't see the harm in adding it, but I can't see it being all that useful unless the President is at an obviously high altitude, in which case many people will suddenly start ignoring the gamemode because they're not aware that it only takes a minute or two to get to that altitude from the ground.
It would be best if it gave you not just his raw altitude, but his height above the ground beneath him as well (so if he's 10 above chiliad, it gives you 6xx for the raw altitude, but 10 for the adjusted altitude/height).