I never thought of it that way for some reason. Always imagined mature quantum computers as being their own system. But it's possible a lot of them will be supplementary components to a classical computer. We have storage-over-PCIe, graphics-over-PCIe, and soon quantum-over-PCIe?
It'll be a long time before they need remotely comparable bandwidth, and more than likely the latency on higher level protocols won't even be near. PCIe would work fine, but so would old school serial.
That seems unlikely to happen in the near to medium term. For that to happen, everything would have to be rewritten using a quantum algorithm and language, and run on quantum hardware. Imagine writing a web browser in a quantum language, within a quantum computing software ecosystem. It's hard to see how that would have any benefit.
If you are talking 100 years out, though, who knows?
