I think Highway will become more popular because of its numerous synergies with cards from adventures.
Highway+Ferry:
Helps to get these highways in no time.
Highway+Artificer:
Any gainer is strong with highway; on-top, artificer does the gaining mid-turn, which can be a significant speed-up.
Highway+Bridge Troll:
Obvious one.
Highway+Ball:
Play Highway, buy ball, gain two highways. Play four highways, buy ball, gain two provinces.
Highway+Inheritance:
It's tough to hit $7 if all you have is highways; but if you're lucky, Inheritance might win you the highways split "7-5", while pseudotrashing estates. Mostly crucial.
Highway+Pathfinding:
Hitting 8$ is even harder, but if you manage to do it, your lab/highway-hybrids will connect in no time.
Highway+Teacher:
Well, Teacher combos with everything, but if you put your tokens "+card" and "+buy" on highway, it's gg.
Highway+Duplicate:
Use Duplicate to gain highways. Later on, duplicate your provinces (or colonies).
Highway + Seaway:
werothegreat described that one: Play a highway, put seaway on highway - all highways get the +buys desperately needed.
Highway+Plan:
Trashing cards while gaining highways is awesome.