I would scrap the nation specific clause; Germany built a railroad from Berlin to Baghdad. Otherwise this is what I intend to experiment with next game, though I was thinking that its OK to rail into contested tts as long as you don’t attack there this turn. That is, you can reinforce by rail, but not attack.
On a more radical note, I was thinking about scrapping all movement limitations in non-combat movement.
So, theoretically, German could rail new units straight to Mesopotamia as long as the CPs control all tts in between, and the destination tt is at least contested and you don’t attack there this turn.
Similarly, the USA would be able to ship units directly to Karelia, as long as the enemy fleet did not stand in the way, and Karelia was Allied held or the move simply reinforced it.
However, mined areas would count as moving into combat so the US would not be able to ship from Washington to Kiel unless Kiel has already been captured by the Allies.