You're treading down a well worn path here, Einstein was down this road as well as you note and got stuck there for the rest of his life. Everybody in the fiel

You're treading down a well worn path here, Einstein was down this road as well as you note and got stuck there for the rest of his life. Everybody in the field would WELCOME something we can measure but can't explain with QM. But there isn't, and not due to lack of trying. Cosmology aside (difficult to measure) all the measurements of femtoscale interactions and condensed matter "constants" and their corresponding QM/QFT calculations that match to like 13-15 decimal places.. there are just incredibly massive chunks of evidence in favor of QM. It's just not a "first approximation" of reality that can be thrown out easily. Theorists and experimentalists in the field come up with new tests every year (they are my favorite papers to read!), so it's absolutely not like there is some inherent scare of not daring to contest it. It's just that you need experiments to contest well-established and working theories, you can't just go out and say "well, but I don't like it".. By the way as I'm sure you know if you studied this kind of physics, the "it doesn't give us any insights into how to peek beyond it" isn't really true, there are falsifiable assumptions that are tested and peeked at all the time - I'm thinking on the hidden variable theorems and validations. The theorems don't assume any specific theory (QM or a new one would do). That road is a nice one to casually drive down.