why wont it be ready for the GENprise? If its going to take 20 years then that is more than enough time, 5 year tests should do then have it manufactured and make variations.
Well, the main selling point for the project is that it can be done using technologies we have right now. Cold Fusion is rising, but it'll still be a while before it can be done on the scale required. That said, it's never been easy to predict technological advances. If it can be perfected in time, that would be great.
Something else that could have potential uses for an Enterprise: graphene. Not only is it the strongest material currently known to exist, but it's also capable of absorbing the harmful radiation the Enterprise would be exposed to outside of Earth's atmosphere.