It's easy to make predictions when outside a field (and I'm guilty of this fallacy too), but easy to miss the true challenges. For example, a lot of people just assume that fusion reactors will be better than fission, because that's what they were told their entire life and because we still haven't figured it out. But looking at energy density or thermal transference and fusion just looks like a really crappy heat source, something that would be incredibly difficult to ever engineer into a product without a secondary invention that is just as difficult, if not more, than the initial idea of fusion.