Louis XXIV
Le Roi Soleil
1UPT warfare is about maneuvers and smart unit movement. Instant air transporting would just remove all marine transporting fun.
Well, it's so late in the game and troops are limited by having one per city. To me, it seems like a nice addition without unbalancing everything else too much. Plus, airports would also be useful as offering bonuses to trade routes, one would assume.
Overall, it seems like a good addition to the game and worth considering for the future.