It's not just superconductivity that you need. You also need to reduce thermal noise to maintain coherence between qubits. mill-Kelvin is the typical temperature range D-Wave computers go to [1], for instance.

In fact, when you see large mainframe-like pictures of quantum computers, the big box mostly contains cooling equipment. The actual circuitry is pretty small.

[1] https://www.dwavesys.com/tutorials/background-reading-series...