"Crypto" is not an alternative to the US dollar so it's adoption will never affect the USD strength as the world's reserve currency. Not to mention that people see crypto as an investment which they mostly bet on the price (they are basically gambling with it) so it is not exactly an adoption to begin with. Bitcoin is also not used at large scale to be considered an USD alternative.
What affects the USD is what can replace it. There are a couple of options from the BRICS currency to other alternative shitfiats that are similar to the dollar such as Yuan. As they are being used more these days, the USD strength as reserve currency diminishes.
So if crypto is "not an alternative", then what is it? A replacement? I get your point that crypto is not big enough to challenge Fiat (yet). But it still does the job it's supposed to (banking for the unbanked). Especially when you can pay for goods and/or services with it. How isn't that an alternative to you?
Some coins have cheap fees and fast settlement times, making them an ideal choice for cross-border transfers. In the case of Bitcoin, it's ideal as a borderless store of value that's better than Gold. It's hard to believe governments will ditch Fiat in favor of cryptocurrencies like Bitcoin and Ethereum. After all, they want to stay in control.
I'd expect Russia and similar countries to build up their own BTC reserves as a hedge against inflation. It will also serve as a "safeguard" against Western sanctions. BRICS will have its very own currency tied to the value of Oil (possibly). They also have the choice of backing their own currency with BTC. Or even Gold for that matter. The world is changing at a very fast pace, so we should expect the unexpected.
