If you want to go off trying to predict the cycle I’d suspect ag/weather tech. Political complexity aside it appears to be the biggest thing we’ll need to work on in the coming decades if we want to sustain the planet’s carrying capacity.

Probably more likely though to be something novel that few took seriously before it demonstrates utility. And this is the issue for QC, we already know what it’s useful for: a handful of niche search algorithms. It’s a bit like fusion in that even if you work out the (very significant) engineering issues you’re left with something that while useful is far from transformative.