Dead thread I know, but for people who have blurry/pixelated widgets with TXAA, I just accidentally found a solution. Dupe your widget material, make sure its set to Translucent and Unlit, then tick the Responsive AA tickbox under Translucency.
Don’t know if that bad boy impacts performance or anything, but it certainly seems to get rid of the AA shimmering on 2d widgets in worldspace.