Jochen,
Great analysis. I appreciate your rare & deep understanding of the issues around QM. I'm reminded of the good advice in your response last year to "focus on observed events", which, yes, I'd done, unfortunately you didn't get to my essay. Yours is flawless (I re-read it to check!) and beautifully written, though QM rarely scores well here, (an exception was my 2015 'Red/Green sock trick' essay).
I very much agree your linking wider uncertainties to QM, something my essay this year also does, even rather more widely! & highlight your 'Toy Model' project to find; "one or more foundational principles such that the quantum predictions naturally follow". Spot on, and this computer plot by Trail 2018 suggests my essay identifies one(..or more). Viz;
Bohr made no 'assumptions' about particle morphology, so had to invent 'quantum spin'. But let's hypothesize OAM as already having 2 momenta cases; Polar Rotation (>0 at the equator {90o} then inverting), and Linear, which is exactly the inverse superposed. I also show both change by CosLatitude. But it's the polarizer electrons we need to apply it to! This needs a new way of thinking about OAM, but Ulla kindly identified last yr it's exactly Poincare's spherical vector distribution! Simple vector addition on interaction at any Tan point gives CosLat output. A 2nd Photomultiplier interaction gives Cos2, with amplitude only above trigger point in ONE channel. Spheres can also rotate on x,y,z concurrently. You see where I'm going with this; A,B 'dials' reverse their OWN findings!!
I hope you might check through it, and also it'll need help from someone with your skills to stand any chance against the "wide agreement..." (your para 1).
Well done for yours. A breath of fresh air and prize candidate. I do hope you'll read mine this year, but also last years; https://fqxi.org/community/forum/topic/3012 (there are also various papers).
My 2010-11 essay '2020 Vision' suggested the 'discrete field model' (DFM) that spawned this may take 10yrs to emerge. No sign yet, but you may the one with the vision!
Very Best
Peter