Quantum Bayesianism

As far as I know, RQM is not even a complete interpretation of quantum mechanics. In the original paper by Rovelli, there are many holes left which I thought nobody has patched yet. If you know of an exposition that corrects those problems, I would gladly read it.

If it doesn't fundamentally change quantum mechanics as a theory, is the picture likely to turn out fundamentally different from MWI?

CI/OR is a different picture to MWI, yet neither change QM as a number-crunching theory. You have hit on the fundamental problems of empiricism: the correct interpretation of a data is underdetermined by data, and interpretations can differ radically with small changes in data or no changes in data.

These are difficult question because we are speculating about future mathematics / physics.

First of all, there's the question of how much of the quantum framework will survive the unification with gravity. Up until now, all theories that worked inside it have failed; worse, they have introduced black-hole paradoxes: most notably, thunderbolts and the firewall problem. I'm totally in the dark if a future unification will require a modification of the fundamental mathematical structure of QM. Say, if ER = EPR, and entanglement can be explained with a modified geometry of space-time, does it mean that superposition is also a geometrical phoenomenon that doesn't require multiple worlds? I don't really know.

But more on the point, I think (hope?) that future explorations of the quantum framework will yield an expanded landscape, where interpretations will be seen as the surface phoenomenon of something deeper: for example, something akin to what happens in classical mechanics with the Hamiltonian / Lagrangian formulations.

On a side note, I've read only the Wikipedia article on QBism and my impression was that it had an epistemological leaning, not ontological: if you use only SIC-POVMs, you can explain all quantum quirks with the epistemology of probability distributions. I might be very wrong, though.

I guess that's possible, but how seriously should we take those when we have no empirical reasons to prefer them?

Doesn' that rebound on the argument for MWI?

Sincere and consistent instrumentalists may exist, but I think they are rare. What is much more common is for people to compartmentalise, to take and irrealist or instrumetalist stance about things that make them feel uncomfortable, while remaining cheerfully realist about other things.

At the end of the day, being able to predict phenomena isn’t that exciting. People generally do science because they want to find out about the world. And “rationaists”, internet atheists and so on generally do have ontological commitments, to the non-existence of gods and ghosts, some view about whether or not we are ina matrix and so on.