The lack of inspectability, it seems to me, would make quantum computing flat-out unacceptable in a variety of problem domains, including pretty much any decision support system. Not theoretically, so much as socially. In the way nuclear reactors are unacceptably risky to many who accept a far higher death toll associated with roofers falling to their deaths installing solar. Sure nuclear saves lives, but my aunt doesn't understand it and she finds it scary.