The existing limits on current density in HTS superconductors are not fundamental, and I suspect they'll improve by quite a bit. (Typical high-Tc wire these days, due to manufacturing limitations, is actually made mostly of silver and other metals, with only a little bit of superconducting material. The other stuff is added for mechanical strength.)

I'm actually not a big fan of fusion research, but for other reasons...

Experiments at Purdue with sonofusion looks promising. Unlike tokomats the strong magnetic fields are not needed. Unlike claimed cold fusion experiments no precious metals are needed. Hot fusion research is a lost cause. They have had over 50 years of experiments behind them and have only produced arguments for more government grants.