Right, but it's also hard to define the "majority" and "minority" coin here. You could define "majority" based on "most hashpower", but say that chain is being mined exclusively by the 3 largest China-based miners, would it still be considered the most valuable? Or maybe only by one miner, like when ghash.io was over 50%?

If the exchanges don't support the concept, it'll still at least be up to the user to figure out which chain the exchange is on.