Problem w/ the ARC reactor is that it is just a design. The real life engineering challenges are still daunting. E.g. for the supra conductors at the Wendelstein 7-X, which provide a much less powerful magnetic field, just assembling and connecting the supra conductor cables for each module was a mind blowingly complex and fickle process that was described at length in this (unfortunately German) super awesome podcast [0].

[0]: http://alternativlos.org/36/