It seems now that Quantum Computing will be a thing in the future, but the stumbling block is outside interference introducing errors into the system. The problem with QC is that it is not absolute. By it's nature Quantum Computing is a bit variable as bits change states.
So, if you run a calculation a couple of times, you may arrive at two different answers, as errors creep into the system.
The issue then, is you have to run a calculation a number of times to firm up any answer. Call the first few goes as uncertain, then as the Quantum computer arrives at answers, eventually it should come away with a result with a certain degree of certainty.
Whether the Quantum computer can perform those numerous calculations and get the result faster than an absolute digital computer is anyone's guess. I mean, how many times do you have to try a puzzle to solve it?
I think that Quantum Computing will have to find a niche. Most likely where you are doing computations that are happy with a degree of uncertainty, or to put it another way where you can reach a level of certainty that is sufficient to do the job.
It's a pretty human way of doing things, because with training we can complete tasks to a high, but not absolute degree of accuracy and still complete the task. For instance we can almost instantly or instinctively estimate the trajectory of a ball to a certain degree in sports and make contact. We just need to figure out what uses Quantum Computing can be put to.