Complicates the memory model by adding operational restrictions that I don't offhand see how to even state within the proposed model. Disables some other otherwise legal optimizations for volatiles. At least some uses can be optimized to no-ops on some machines. Complicates the memory model by forcing it to take account of special library functions. Complicates the rules for optimizing code.
Usages seem amenable to mechanical sanity checking.
Supports the most controllable and optimizable code of all options. Even if adopted, it would probably take several years before you could write portable code employing it. Scrap LC-based approach. Requires a different solution to all the problems with JLS approach that LC solves. I'm still hoping that there are better undiscovered options.