I dont know if this is off topic but Gaijin should add non controversial state/provincial flags 1. because money, 2) they do sometimes pop up time to time by soldiers who live there irl throughout history. Some of them might not be the smartest to add though.
Overall not every country seems to have provincial or state flags or something close to them but they would be nice to have in game including the Puerto Rico Flag. I don’t see this as an issue for 89% of the cases. There are some historical provincial/state flags world wide too that where decommissioned for differing reasons and might be case by case. But having old flags like the old Canada flag which is now the flag of Ontario would be nice to see as a decal if its not already. I think Japan’s prefecture flags would be popular.
Gaijin has lots of opportunities here.