One advantage of stablecoins is price stability. Merchants don't have to worry about price volatility when transacting in stablecoins. In the past and present, there have been a handful of projects proposing issuing altcoins (non-stablecoins) that will lead the future of crypto payment. What's the fate of such projects, will there ever be considered viable?
You have stated rightly that stable coin do have price stability. But does it not interest you that merchants online or offline do not worry nor ask for payment in stable coins.
Rather they request payment in Bitcoin, Litecoin and Etherum amongst few platforms i have come across.
We cannot consider or judge fate of other projects, because an altcoins growth is not dependent on them been listed on a crypto merchant payment webpage.