[throwup238]

Cuprates are also brittle ceramics so they’re difficult to shape and larger pieces and assemblies tend to run into issues with grain boundaries that interfere with superconductivity, so there’s a lot of practical issues. The classic superconductors are very low temperature but are much easier to cast.

[FredFS456]

There's a few fusion startup companies using superconducting ReBCO tape to make their magnets. From the results that they're getting, I think we've largely cracked the engineering problems of making "wire" from ReBCO and it's largely just a scaling game now. I do want to point out that they're still cooling with liquid hydrogen at ~20K for high current capacity though.

[cyberax]

I invested in a couple of fusion startups (because why the hell not?), and the word on the street is that flexible tapes/wires are still not a solved question. Nobody can make them with consistent quality in large enough batches.