New units

The cargo plane has been suggested a lot of times.

In truth it transporting troops by air never has been a thing in WWII so it will never be integrated in the game.

The only air troop transport in WWII was paratroopers and we have those already now.

I think that railroad transport would be good idea(cargo trains). Just to add option for building railroad infrastructure that would transport all units at same speed. That was big part of WW2.

Has been suggested also a large number of times. But in WWII train lines were very frequently bombarded or sabotaged by the resistance. Anyway, all means of troop transport including transport on trains is already taken in account in the current movement time.

Marines

Infrastructure takes care of movement speeds providing a quick and cost-efficient way to drastically transport troops to front lines.