Erik - you raise a lot of interesting topics!

On smaller and newer reactor designs, they have merit IMO, but I am hesitant because nuclear waste is problematic: anything that has been involved in fission will have a lot of short half-life isotopes - i.e., be very radioactive. But then again, nuclear waste is not the huge problem it is made out to be, because the volume is so low. It _IS_ a problem, but not a show-stopper. I am personally worried about any fuel cycle that produces fissile material that can be chemically separated (e.g. plutonium), and then used to make bombs.

I think that once we figure out how to make a fusion reactor work, it will quickly become a lot simpler. And will create designs that are easily manuctured. E.g., look at how SpaceX has created a rocket assembly line for their new "Starship" rocket - radically reducing the cost of something really complex. They are doing the same thing for the engine - the most advanced rocket engine ever made, but their goal is to create two a day in volume.

I agree that it is hard to imagine a fusion or fission system being practical for a car. But battery technology is nowhere near its theoretical limit...

I think that fusion has a great future for spacecraft propulsion. It is a simpler problem, and there are several initiatives trying to create a fusion engine. That would be a game changer for travel within our solar system. It would make the asteroid belt highly accessible, which is necessary for some of the "big plans" that China and others like Elon Musk have. It would make big projects, like building huge structures in pace, feasible.