If we had someone making GaAs processors in the 1980s for a price competitive with their silicon counterparts and with a long-term roadmap, we'd have very different computers now. And some extra toxic waste problems.
You should still view anything Quantum as early R&D.
The good thing is that someone who can make lots of chips can reduce the effort it takes to do R&D. With more people researching possible applications, it's likely we'll progress more quickly.
and what are those applications?
Of course, the plan is by the time quantum computers become capable of breaking those algorithms in practice, the industry will have moved to post-quantum cryptography algorithms.
But there will still be legacy systems which haven't, and also encrypted data recorded in the past in the expectation they'd be able to decrypt it in the future.
- breaking a lot of traditional public key crypto (this gets a lot of attention, but its not that big a deal because there are alternatives)
- in theory i guess quadratic improvement on unstructured search. I think its unlikely to be practically relavent.
The algorithm engineer is so in love with the idea that an algorithm is the solution to everyone's problem (its a natural human bias to think the world desires what we have) that they way overweigh the importance of route planning improvements which are incremental or worse - would be thrown away because the practicalities of implementation doesn't warrant the marginal improvements.
Our problem is similar (but not identical) to the traveling salesman problem. We run on a tight time constraint (measured in days for the complex type and measured in minutes for the simple type).
We're running approximations on classic computers but estimate that we'd save billions if we could reach optimum.