Now, Max2021 is out here's a list of what i think is missing to make the view port a fully fledged real time rendering engine alternative:
1. Direct Vertex Color/Map display, without need for baking.
2. Real time Glossy Refractions.
3. Real time Subsurface Scattering, single/multi, with forward/backward controls.
4. Real time volumetrics for environment fog, lights and objects; VBDs would be a plus.
5. Shading Displacement; surface or volume based.
6. Parallax and Signed Distance Field OSL maps.
7. RTX support for real time GI, shadows, reflections, refractions.
Thanks,
Greg