It will be interesting if they can pull it off. I wish the article would have given a few more details, i.e. the average width of a fjord. Got to be a ton of engineering issues to deal with, but if they can work it out, it would be cool.
Cost effectiveness isn't necessarily their first concern, Norway is comfortably rich, to say the least. But if you have fjords a kilometre deep, kilometres wide, surrounded by mountains of similar height and often made of granite, you got to come up with solutions.
I spend months there each year and it is already impressive to see the network of bridges and tunnels they have. Some of these tunnels have roundabouts and intersections in them, some spiral up inside a mountain to spit you out hundreds of meters above where you entered them onto bridges which then span fjords far beneath them. Some go down and up in steep angles deep below the sea.
It's quite a driving experience but it still takes ages to get anywhere. Count on an average of no more than 60km/h and due to the coastline distances often are much larger than you'd think at first. You're even slower than that if ferries are in the deal and they often are.