Cryengine actually combines MSAA 2x with Temporal AA, they call it SMAA T2X, and it is proof that MSAA in a deferred renderer is completely feasible, the UE4 devs just don’t want to be careful in their shaders and deciding when to use sample-frequency vs pixel-frequency, here’s the presentation: http://www.crytek.com/download/Sousa_Graphics_Gems_CryENGINE3.pdf
It explains how to minimize perf impact of MSAA with custom SV_Coverage, how to do temporal reprojection right so that there’s very limited ghosting, etc.
The latest ‘build in VR for VR’ UE4 video (Build for VR in VR - Unreal Engine) shows INCREDIBLE TXAA artifacts on the 3d widgets because they are constantly jittering (motion controlled), because ue4 couldnt care less about having correct motion vectors (how long did it take to generate correct motion vectors for world displacement ? and we still dont have custom motion vector output in materials for things like UV-scrolling textures).