Don't be discouraged if what you produce initially is something other people dismiss as a toy. In fact, that's a good sign. That's probably why everyone else has been overlooking the idea. The first microcomputers were dismissed as toys. And the first planes, and the first cars. At this point, when someone comes to us with something that users like but that we could envision forum trolls dismissing as a toy, it makes us especially likely to invest.(http://www.paulgraham.com/organic.html)
> you can't use this currency for day to day transactions
Not with this attitude, you can't. ;)
What currency is "this"? BTC, ETH, Doge, USDC, DAI?
> incredibly volatile
How volatile is USDC, DAI, GUSD?
> risky to hold significant amounts of it
It's also risky to walk around with significant amounts of cash in the wallet. It doesn't stop people from wanting to carry some money around. And more importantly, the alternative of "going cashless" is a whole other set of systemic risks.
> it might be useful!
The use cases exist already. Micropayments and streaming transfers (as an alternative for subscriptions) using stable currencies are already possible. If you don't care about it, it's a different story.