I've tried just about every combination and permutation of post process AA injection possible. FXAA + post process TAA (which needs a shader to extract motion vectors that is then passed to a TAA shader) can do ok, but is so expensive and adds so much motion blur that more supersampling is usually preferable.
Without native motion vector support the only easy improvement would probably be more aggressive versions of the SMAA and FXAA presets they already have, but it would add a lot of blur and barely smooth the worst offenders of the specular aliasing that is most noticeable. If they can find a way to reduce the contrast of these edges, that would probably help more than stronger AA shaders.