Note realism has particular meaning in physics which means there are properties even between measurement. So Einstein can even believe a world existing with merely spin as the observable can be put under realism so long as it has deteministic values in between measurement. Einstein is so advanced with his spacetime physics but why couldn't he go one step further and believe there was no properties before measurement. Maybe because it can falsify his spacetime idea. So the incompatibility between QM and GR already started in the Bohr Einstein debate in 1927 at the Solvay Congress. But at that time, they never plan to unite QM and GR. Did Einstein plan to do that? I wonder what year was this attempt at unification of QM and GR become a serious endeavors or programme. Anyone?btw, in reply to your comment in post #1 about Einstein's reluctance to give up realism, there is a famous quote attributed to Einstein from a discussion with Heisenberg, where Heisenberg was making a similar point to you and Einstein replied that the abstraction of spacetime was all nonsense, and not to be taken literally, just a mathematical framework for making predictions of nature.