Well stablecoins by design cannot really fluctuate a lot in value (unless they collapse), so speculation on them is pretty much out.

It's still pretty unclear to me why you'd actually want a blockchain for managing it though, rather than a traditional database hosted by the central bank that is responsible for the currency that the stablecoin is following. You'd get vastly more throughput at much lower costs, and it's not like you really need decentralization for such a system anyway. The stablecoin is backed by something the central bank already has authority over.