The 4 minute mile was a mental barrier. The sub 2:00 marathon is a physical one.
Sub 2 is only a question of when. People thought 4 couldn't be broken. Once the mental barrier is broken, it becomes possible. Consider the progression of the marathon. In a decade or two, the record has gone down 3 minutes in less than 2 decades. Almost 7 minutes in the last 4 decades. It will go down someday, the progression will be slow though. Maybe 2:02 by 2030 2:01 by 2050 2:00 by 2080? Who knows, but there's no evidence to suggest it can't happen other than that Bekele is the current GOAT and can't hit it. Viren was an king in his era and now he would be an also ran because of how much the sport has progressed.
At the time of the first sub-4, the 880 WR was 1:46. The 4:00 mile was easy pickins, as evident by how many broke it within a short time after, and how quickly the WR came down shortly after.
No one has even run 30k at 1:59:59 pace. That's like saying the sub-4 mile is close when the WR for the 800 is 1:57 and the 1000m WR is 2:30.
Not close. Won't happen in the next 50 years.