Fortunately, they have more important things to update/fix than this...
...actually, what would be more useful is an upgrade for Bombers (available to everyone, of course, like the other unit-specific upgrades). Air: Main Attack is the only standard unit that does not have at least one upgrade. I figure that any one of "long-range bombers" (fast +1R), or "heavy bombers" (lucky +1CC), or "flying fortress" (+1D) would be cool in my book!
Back to the OP: do your own map, and make a unit called "flying submarines." Or do a World Map clone, like I did...I have 4...three are ongoing experiments with unit development: "Strategy Heaven," "One of Everything" and "Kitchen Sink." The fourth, "RatWar's World," is going to be my penultimate unit selection, based on everyone's experiences with the other three clones.
My clones also have a few city changes - I added the port city of Norfolk to USA Atlantic; I made Philadelphia a port city; I added Juneau as the capitol of USA Alaska; and I added Tijuana to Mexico as a port city, just south of the border from San Diego. I also changed a bunch of cities from "extra" to normal (always present). Once I get around to learning how to draw borders, I'm going to split India into a North and South, where the southern capitol would be Mumbai.
All of my clones are published, so anyone with Premium can host a game on them. Try them out, or join one that starts. I always keep 2 or 3 casual games going at a time on at least one of them. Please PM me what you like/don't like. I'm always open to suggestions!