I dont expect this idea will work for the AI but it could make playing as the allies or in multiplayer games much more interesting.
I've been thinking about transport ships and how to make more use of them. What about creating a unit such as Lend Lease bomber this unit would have a movement of 1,act a land unit and be much cheaper than an actual bomber.
This unit could be loaded into a transport and when unloaded into a city with a specific improvment the lend lease bomber gets converted into an actual bomber.
I would suggest you could do this for a few units like tanks, artillary, fighters and bombers.
It would also be nice if you could unload into other nations cities with the required improvement and they get that type of unit.
Interesting Idea ? or have I got too much time on my hands ?