Combined with the recent LK-99 frenzy, my impression is there's a lot of room at the bottom, as someone famous might have said.

Not in the sense of nanomachines, but using modern materials science: deliberate and reproducible crystalline construction, informed by large scale QM modelling of EM material properties.

AlphaFold consumes, and improves on, raw electron density functionals (EDF) for protein folding. Perhaps there is scope for similar improvements over existing methods for modelling and exploring the space of metallic or complex salt crystals.

Most of the advancements in technology ultimately trace back to materials engineering breakthrough.

Even just 2x or 4x higher energy density batteries would have a tremendous impact on electric aviation and drones, phones, and so many more things.

Sw with super conductors except that would be even more exciting, and we would get a new generation of incredibly sensitive sensors and antennas.

I could go on and on but the main point is like what you said, the materials drive the breakthroughs in innovation if technology (in many cases)

Neutrons whizzing through the Erbium matrix don't ever strike those nuclei? Would think that would tend to get a little 'hot' over time.