I've visited a company that produces classical and high-temperature superconductors, though this was quite a few years back. I don't know the exact market size,

I've visited a company that produces classical and high-temperature superconductors, though this was quite a few years back. I don't know the exact market size, but the MRI and NMR markets are probably not that small, though they use almost entirely classical superconductors right now. But they have hit the physical limits of classical superconductors in NMR, and the first NMRs with high-temperature superconductors are produced and sold now. So there might be some more development there even without the fusion angle. One purpose of the support material that isn't super-conducting is thermal protection. If your superconducter quenches, you have to dissipate the energy contained in it without destroying the magnet. In classical ones they use copper wire around them as far as I remember, and the high-temperature ones are a very thin film of ReBCO deposited on metal tape, so the actual superconductor is always a small part of the material.