It was my occasional habit in the pre-covid times to crash conferences on the interpretation of quantum mechanics. The field is relatively small and so the conferences are surprisingly welcoming, even if you are a bit of an outsider.
A few years ago I went to a conference in Long Island called “Quantum Mechanics: Paradigm or Ontology of Nature?” where I met one of Fuchs’ grad students (whose name escapes me at the moment.)
I can try to express my problems with qbism in the following way. Consider that special relativity in particular is a relational turn in physics. Einstein’s main idea was to recognize that certain apparent quantities were frame dependent and therefor ontologically suspect (presuming that one’s frame of reference doesn’t matter) while other quantities (perhaps not the obvious ones) were frame invariant. QBism tries to suggest that the outcome of certain experiments has the same character - certain sorts of quantum mechanical measurements give fundamentally frame dependent results which is why different observers can have different accounts of, for instance, when a wave function “collapses”. They would argue that wave function collapse itself is an ill posed idea.
So far so good, I guess.
The issue is that special relativity identifies the true observables (things which transform appropriately under the Lorentz group) and then constructs genuinely new physics out of them. Physics which doesn’t just explain why certain non-invariant quantities look the way they do in certain frames (boring) but also explains why gold is, for example, yellow. That is, identifying the true frame independent quantities leads to a new framework of physics which allows us to calculate new things.
Its this second part that qbism doesn’t seem to offer anything towards. Yeah, its easy to say that measurement outcomes are in general not frame independent in quantum mechanics but that doesn’t really lead us to any new physics (so far). Like I said, I’m pretty sure that Quantum Mechanics is not close enough to a real theory of the world to even be useful as a philosophical tool. I’m also pretty sure that QFT isn’t well understood enough or well posed enough to constitute a genuine basis for philosophical discussion either.
All this seems to be related to gravity, which has its own pile of philosophical problems. I have a totally intuitive hunch that this nut won’t crack until we understand quantum gravity.