Interesting idea. I agree that Urban Native American and Nomad Native American should be in different groups.
The restriction for Nomads would be the one already said here, less tech but combat bonus against higher tech and may also get techs from killing units; perhaps also giving settlers extra movement or something.
Then, Urban Native Americans shouldn't get less tech; just probably make oceans impassable, and horses unabled until meeting another culture group. In exchange, bonus for wonder production in the capital; and extra tourism. (Which is going to be interesting, Urban NA would be influencing the local cultures, but all that tourism is still in no effect until meeting other culture groups)
As for Colonial... Somehow I think ideological pressure, or something related; can't think of something specific.
The restriction for Nomads would be the one already said here, less tech but combat bonus against higher tech and may also get techs from killing units; perhaps also giving settlers extra movement or something.
Then, Urban Native Americans shouldn't get less tech; just probably make oceans impassable, and horses unabled until meeting another culture group. In exchange, bonus for wonder production in the capital; and extra tourism. (Which is going to be interesting, Urban NA would be influencing the local cultures, but all that tourism is still in no effect until meeting other culture groups)
As for Colonial... Somehow I think ideological pressure, or something related; can't think of something specific.




. The wide range of inclusion is mostly because I personally have as many custom civ mods active as I can for the YnAEMP, and with so many civs its nearly always a fresh experience. But unfortunately, it won't be any easy process for others to make compatibility, so I'll endeavour to be as inclusive as possible. And some of these civs I didn't realise were already mods. You must have really dug deep to find them.

) and all those ideas. I'll try figuring something with other groups, now when I can compare my ideas with these 