Niemand
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Haha, they've been working on controlled nuclear fusion for ages, and they're barely making any progress, and you want a PORTABLE reactor, like in Iron Man... Well, I don't know what will happen by 2045, maybe they'll get lucky and come up with something.
Portable nuclear reactors already exist. They're the size of a room. And by 2045, they'll make them even smaller. Or they'll come up with something new.
But the idea of using all sorts of exoskeletons doesn't really inspire me.