Last summer I traveled from Skagway to Juneau. My airplane was delayed because of weather and I overnighted in Skagway, hoping to get out the next morning. Next morning there was a lady from Skagway on board who was flying to Juneau to catch a flight on to Anchorage. When the airplane landed in Haines, we picked up a man from Haines who also was flying on from Juneau to Anchorage. Once in Anchorage they would both need to come home again, most likely by air. They had chosen to fly knowing they wouldn't have a car to drive while in Anchorage.
Both these folks had the opportunity and ability to drive directly to Anchorage, but chose to fly instead - each even waiting an extra day for the flight. It is, after all, at least a day's drive from either place. This choice is very common according to the air service. That sure makes me wonder how many folks from Anchorage, Juneau or the Interior would choose to travel more than once or twice by road to or from Juneau.
My personal conclusion is that any road from Juneau to a northern connection will be largely for the benefit of summer tourists.