I suspect that many answers to this will involve StarTrek or Star Wars fantasy, substituting that for “theory”.
The two biggest things that I think could eventually be developed are cold fusion and room temperature super-conductors. These would revolutionalize our way of life and be Nobel Prize worthy.
For the near future, we may have to settle for better batteries and some sort of biofuel that does not cost more to manufacture than it outputs in energy….Cheers!!