I would say that all proposed highway ways should probably be deleted unless we know those roads are going to be built and their eminent construction is within a more reasonable timeframe where plans are less likely to change. The OSM Wiki even seems to hint at discouraging mapping proposed highways that truly are only in the proposal phase: https://wiki.openstreetmap.org/wiki/Tag:highway%3Dproposed

I personally have been going around deleting some of the ones I originally mapped myself, just because the data doesn't render and isn't used by anyone because it's not really mapping what's on the ground and can only be used as a sort of note as pre-mapping for upcoming construction in the near future.

Considering we don't have an actual date for construction of a freeway (if that even happens), I wouldn't worry about retaining or restoring anything here. If we consider how long it took for the Beltway to be built, or for how long it will take to get to building the 395 spur in Reno, we're talking about a project that, if confirmed, is likely so far into the future that there's a chance either one of us may not be interested in editing OSM anymore by the time the first shovel hits the dirt.