My guess is that initially it will get eaten away by parties that currently trade in US dollar for convenience shifting to trading directly in their native curr

My guess is that initially it will get eaten away by parties that currently trade in US dollar for convenience shifting to trading directly in their native currencies. It's a pure cost / risk equation for them that they have to manage this third variable in their dealings and if that outweighs the benefits of using a common currency they will make an agreement to trade directly. This will happen slowly over a long time and eventually a new default currency will emerge as a result of these decisions.