I have driven that stretch in eastern Montana many times, and I have also driven that stretch of road in Texas. One thing the article doesn't mention about that toll road in Texas is that it was very expensive -- over $5 if I remember correctly. I tried it once not knowing the cost, and it was a lot of fun to drive on. But for that price, I can see why so few people use it, especially since you have to go out of your way. I was on my way from San Antonio to Dallas, so I didn't mind skipping Austin.
As for eastern Montana, the countryside is very open with gently rolling hills and long stretches of mostly straight sections of Interstate. Very often, you will not be able to see a vehicle in either direction (and just as often, no more than one or two buildings either), so the temptation to cruise is very high. Any wildlife can be seen from miles away, and there are very few trees. My only concern would be raising the speed limit on the western side of the state where there are more mountains and forests. There are some highways with 70 mph limits with limited visibility (both on the road and in the underbrush around) that makes for dangerous driving. As long as they take these things into account, it makes perfect sense. Montana already takes over a day's driving. just to get across.