The other thing we don't know is whether it's physically possible to build a quantum computer capable of it. As opposed to a theoretical ideal quantum computer.

The other thing we don't know is whether it's physically possible to build a quantum computer capable of it. As opposed to a theoretical ideal quantum computer. The thing that gets smoothed over with QC is managing the error rates and the fact that it hasn't been shown to be physically possible to scale up computation without the error rates also scaling up exponentially and making the thing useless.