Uncentralizable energy overproduction would help.
We have to make it work before we can optimize it. Fusion still poses many engineering challenges that have nothing to do with the quality of our superconductors. How to not melt the reactor walls and what to do with all those angry neutrons, for starters.
The vast majority of their size, weight, and cost is related to maintaining extremely low temperatures for the superconductors right next to the angry neutrons.
If you could use a regular coolant loop with heat pumps and only needed to maintain, say, -20°C, it'd be much easier to keep the superconductors cool and transport away the neutrons' heat.
Point is, even with better superconductors we'd still be a long way from practical fusion power. They'd be a step forward, but they're not the key that's going to unlock a world of cheap clean energy.