You want a use case for mobile quantum computing power? Here:

One problem quantum computing presents is that its computing potential overrules all current encryption mechanisms right? If your beautiful centralised computing solution can easily decrypt any data stream encrypted by conventional means then you’ll probably need an equally advanced solution to encrypt your data.

Another: a mobile running a 20-year-in-the-future graphics/physics game engine to simulate an AR reality over 10G internet together with 40.000 other players using the 20 different cameras in your phone that observe x-rays throughout microwaves while streaming to your 4D headset.

I’m certain there are mathmaticians and IT scientists out there who can elaborate on why this is/isn’t a bs use case. My point is that if I can come up with a potential use case in seconds while I’m cooking diner, then it’s plain dumb to assume that TONS of people won’t come up with actual use cases in the coming 20 years.