A limitation...at ambient temperature and pressure. Usually this is an optimization frontier, where something that has tetchy critical current/field at high te

A limitation...at ambient temperature and pressure. Usually this is an optimization frontier, where something that has tetchy critical current/field at high temperature is going to have very good critical current/field at the same temperature as a lower-Tc superconductor. If it superconducts at all at room temp, cooling it down even to 200K (about dry ice temp - quite cheap to do) could get you something very usable.