Came across this issue while modifying the Ski Resort. Right now, any yields associated with a mountain improvement (like the Ski Resort) only appear for the Inca because of their UA to work mountain tiles.
Basically every mountain improvement mod will therefore have to make the change to make the respective modifier available to all civs, maybe linked to a certain tech (I'd propose mining).
I think it would be a good idea if we were to agree on some sort of community resource for that which can then be used as dependency by the respective mods.
Since the +2 production are a separate trait of the Inca, there wouldn't actually be any gameplay difference until the moment a mountain tile got a yield from another source. Of course, people would be free to add default yields to mountains with their own mods then.
Basically every mountain improvement mod will therefore have to make the change to make the respective modifier available to all civs, maybe linked to a certain tech (I'd propose mining).
I think it would be a good idea if we were to agree on some sort of community resource for that which can then be used as dependency by the respective mods.
Since the +2 production are a separate trait of the Inca, there wouldn't actually be any gameplay difference until the moment a mountain tile got a yield from another source. Of course, people would be free to add default yields to mountains with their own mods then.