Dear Israel,
Einstein's brilliance is the greater because of his intellectual honesty. He was always thinking back about the implications of his theories and if need be revise them. I think his attitude to the ether was ambivalent as you point out, but he needed it for GR in order for his grid of clocks and measuring rods to work (I am paraphrasing his words).
I agree with you about Decartes and highlighted his ideas about ether (together with his amazing illustration of the ether vortices) in Section 2.3 of my Beautiful Universe paper. Maxwell's gear-like mechanism to model electromagnetism in vacuum suffered the same neglect that befell Decartes' idea. My Beautiful Universe lattice of nodes with angular momentum in units of (h) are my way of recasting these ideas into modern physics.
Your sentence "if relativity is not accepted as a physical reality but only as a geometrical model, then one can argue that the marriage with QM is an illusion" is too general to understand in the context of what I said. Are you objecting to what I said about the need to reexamine some of Einstein's other ideas as you have done for AS? I am not saying relativity or QM do not work, but that they works despite their being so abstracted from the simple physical way I think Nature works at the tiniest level, a level that assumes the absolute space idea that you have so ably defended.
Best wishes
Vladimir