There already are some useful JJ devices, just not for conventional computing.Don't get me wrong, I'm sure there's plenty of very significant (possibly even insurmountable) problems that will have to be worked out, before/if we ever see real, useful devices using JJs.
Modern chip manufacturing is hitting brick walls due to the size of individual silicon atoms. Trying to work with crystals that are 100+X bigger than individual Si atoms is bound to pose some rather quite serious challenges. No superconductor, no JJs.
And my point was that quantum effects on low-density cryogenic superconductors likely won't survive the transition to room temperature or high density.My point was simply that the potential advantages of a real STP superconductor aren't just limited to the obvious one, namely, the removal of losses due to resistance.
If the funky cryogenic quantum stuff doesn't work at room temperature, then all that a room-temperature superconductor has left to look forward to is reducing ohmic losses in whatever is worth using it on.