[quote=kewp]
But there’s the catch, why would they want to dump a currency that is gaining purchasing power against everything else? [/quote]
They might well be inclined to bias against adding more of a currency that has recently gained purchasing power.

No one will fully divest their foreign exchange reserves of dollars. Doing so, particularly when they hold nearly two trillion dollars, would devalue the remainder of the holdings; not even the largest market is that liquid.

They might do it solely for purposes of diversification. A trade-weighted or GDP weighted currency basket would hold only about a quarter in dollars.