I don't know much about fusion. It seems that the breakthrough they're talking about is that reactors are ~10x smaller. Why is this a big deal? Square footage is plentiful. I thought the problems are safety and how much energy it could produce.
One big difference is the smaller the device, the quicker and cheaper it is to iterate. If it takes 15 years and $X billion to build and test your device, then progress gets measured on a per-lifetime instead of per-year basis. If your device can be built in a year and for $X millions instead, the testing and debugging can be done much faster. For a software dev comparison, think waterfall versus agile.
If it's 10x smaller it is available for portable applications. Like boats/planes/space ships. It would also presumably be easier to air drop in developing regions to bypass building a giant energy grid (similar to cell phone deployment).
I think it's less about the size in square feet than the size in dollars (including installation, maintenance, and waste disposal). The pool of people willing to buy a $100M device is small. The pool of people willing to buy a $10M device - even if it's less efficient - is much larger. That makes it a potential revenue source, instead of an eternal revenue sink. Much as fusion doesn't become technically useful until energy output exceeds energy input, it doesn't become economically useful until revenue (for its maker) exceeds cost.
That's a 20 year old 1GW combined cycle gas plant, in a building roughly 50mx150m. Anything they can do to bring fusion plants smaller than ITER is going to help.
