Bleh! Is this true? That sucks. Why do the programmers insist on hard coding everything? Why can't it be an option in the editor?
Hidden Nationality land units are great. You just have to make them underpowered and only available for a short space of time. Right now, in my current PTW game, I'm watching some border skirmishes between the Scandinavians and the French. The French are sending partisans (Hidden Nat) at the Scandinavians who are repelling them with their tanks. The French will never capture a Scan city because the partisans are not strong enough but they will certainly keep trying which makes the game fun. I'm afraid now the AI will build them rarely if ever because all they can do is raid some workers and pillage some tiles. Man this has the potential to be awful. This has the potential to keep me in PTW. You know how boring times of peace can be? Have a bunch of underpowered HN units and it's never boring.
If "invisible" is actually fixed so that the AI can't see your invisible units then great. But neutering the HN units stinks. I hope it's not true...