However, what a lot of people don’t realize is that stablecoins fluctuate in ‘price’- or rather, purchasing power- as well.

You'll need a better argument than that. Fiat money in stable polities vary predictably enough to be used as money, in part because they are managed by humans under sufficient professional and political pressure to keep them adequately stable. The choice of a unit of account is essentially Darwinian. The most stable currency wins. Therefore, unless XNO is more stable than its fiat competitors, it won't become a unit of account, and, therefore, will remain a way to move fiat, not a replacement for fiat.