“ There is no prospect of a replacement for the dollar in the foreseeable future.”
It already exists. It’s called crypto currency. Most likely Bitcoin.
“ Trade among BRICS countries is too small to sustain a common currency.”
They make up the majority of global trade.
“ It only makes sense to trade in national currencies”
Why? You do not base this conclusion on any evidence. All major currencies are fiat – it has no intrinsic value. Currency is just a medium for the transfer of goods and labor between two parties. A “national” currency only has the advantage of being forced upon a nation of people. Otherwise, if not used, it’s worthless.
The best currency is one that’s used the most frequently. So an “international” currency by that definition is far more advantageous than a “national” currency. That’s usually referred as a reserve currency – which is what the USD is now. But the US, like every nation before it, abuses the reserve currency.