I really hope he does this. It would force countries to choose between G7 and BRICS, and the latter is where pretty much all the manufacturing happens making it indispensable. This would play out exactly the same way as trying to shut Russia out of the global financial system did, but on a far bigger scale.
The mere fact that Trump is floating this idea is an indication of panic as well. If the US wasn't worried then there would be no need to use coercive measure to keep people from fleeing dollar based system. These kinds of mob tactics that will further convince countries that they need to move off the dollar as quickly as possible.