One of the main objections to the pilot-wave theory of QM is that it brings us back to the idea of a "luminiferous aether" that was famously disproved by the null result of the Michaelson-Morley experiment. What would the substrate be? The article gives a very brief hand-wavy mention to it being "space-time" and I've heard this before, but I have yet to hear even a good suggestion for how this might work.

A related problem is that both De Broglie's and Bohm's pilot-wave models leave open the possibility of "empty waves" that carry no momentum or energy and are not related to any particles. Even if we assume that it is space-time through which they propagate, this gives us another piece of math that we need to just throw away, similar to the non-observed probabilities after state collapse, which runs counter to the goal of creating a formalism where the math corresponds to something real in the universe(s).