I think that anti-gravity or being able to harness it to create a gravity field is the pinnacle of propulsion. There would really be no reason to replace it, although planes are inherently limited by the pilot, it's only a few years until we see more and more remotely piloted vehicles. It overall just makes sense, take the risk, enhance the performance to the structural limits of the vehicle, not the person.
I think solar is the next boom efficiency is the main problem with it now.
A bit of a tangent, but then again everytime humans have tried to forecast the future we're way off with expectations both ways. We think too much into what we have now, and not enough into what doesn't exist yet.
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