Not a what, but a who. All the old fogey engineers, engineering managers, and just managers in general. But as to which current ideas will see fruition in 30 or 100 years, well if I knew that, it might not be 30 years, now would it. It might be that it would take that long for the ideas to be worked out in full and then accepted, or it might be that they can't be implemented with current technology, but with some other as yet unknown theory, or with a need in some other area, the technology might be available in 30 or 100 years.
As long as it's physically possible, it will get done, someday, by someone. Although economics could put that day way way into the future.
Economically viable enters into it as well. Just some guesses though:
1) Cars that drive themselves
2) Space Elevator
3) Quantum effect transistors (ultra-small switches at the limit of Si manufacturing. I'll bet real money on this one happening.)
4) Quantum computers (Not the ultra-amazing computers that some people think, but they will be able to make P=NP, which will be a huge improvement.)
5) Huge advances in medical technology resulting in lifespans typically around 100 years for people born at that time.