I was just reading some posts speculating how long the climb might be on the mountain route and I had the following two ideas:
As zwift is a constructed 3d world the mountain climb could still rejoin the rest of the route without a massive downhill. It does not have to conform to reality - you could even make some kind of portal. Sitting on a turbo doing a down hill after 60 mins of climbing might be a bit dull.
you could have different turn of points so people can do different length climbs - 10,20,40,60 mins ect.