In my opinion, we should map things only "when the shovel hits the ground" sort of thing, when the actual work that affects people on the ground happens. Using this approach not only eliminates the ambiguity and uncertainty when looking at the map and certain maps/routers don't easily distinguish between existing and planned/proposed features, but also decreases the amount of effort we have to put into keeping the map current. You mapped this proposed plan, but then nimbys will complain and DOT will have to revise that proposal, which you'd have to update once again(?), then update it again when they finalize it and start actually building and then update it again when it's actually done.
On the other hand, map it once when the construction starts and update it once it's live...