There's plenty of other optimization methods out there, simulated annealing for example. SGD just lends itself well to the massively parallel architecture of Nvidia GPUs, that's the only reason why it's so prevalent in the industry.

eh who cares about quantum models, too much incoherence and noise. D-Wave's adiabatic quantum computer is showing a lot of promise in the optimization arena. All that needs to happen is a quantum method used for finding good classical ANN minima instead of SGD; then there would no longer be the requirement for lengthy and costly GPU training if quantum annealing of ANN weights becomes a reality.