It's already been happening. Trade in real, rinminbi, rubles, rands or rupees.

Russia reduced its dollar reserves (and even paid Trump in cold hard dollar currency in a briefcase for refueling the plane in Alaska which was hilarious because they're banned from the dollar access)

China has been severely reducing it's dollar reserves, and I guess after the whole India thing, the Indians are reducing that reserve currency as well.

Demand has dropped significantly