But that's what I meant! I didn't make the connection of those links to fusion. The OP did!
It could be. Our aim isn't getting to some high energy, but rather the GAIN in energy. About 2 months ago, we managed to get a significant milestone in which we managed to show a 100 MV/m gradient in the wakefield generated in such a dielectric accelerating structure. Note that a conventional copper accelerating structure can only manage up to 40 MV/m. This could lead to a more efficient and compact accelerator, just the type mentioned in the OP.
It is significant enough that our funding agency immediately agreed to pay for the "accessories" needed for a second Klystron that we planned for.