I think with some, like myself, who only wear the kilt because of a connection with Scotland and a clan, there wouldn't be much of a point in wearing a non-Scottish tartan. I have a kilt because of a pride of being connected to a particular clan, and when I wear the kilt I am reminded of that. If I wore a kilt that is new and local, I'd only be reminded slightly of my connection to Scotland in a general way. Yes, the connection is now distant, but memories are long. This is only my opinion, but your question is a good one.