But that theorem being true doesn't mean "they will work given enough time". That's my objection. If a setup is physically possible but sufficiently thorny to actually build, there's a good chance it won't be built ever.

In the specific spot I commented, I guess you were just talking about the physics part? But the GP was talking about both physics and physical realization, so I thought you were also talking about the combination too.

Yes we can probably test the quantum theory. But verifying the physics isn't what this comment chain is really about. It's about working machines. With enough reliable qubits to do useful work.