Masters success is a combination of two things:
1) Base ability
2) Longevity
Having one doesn't guarantee the other. The best masters runners have some combination of the two.
A runner who excelled as an open competitor can find success as a masters runner even if his longevity is average, because even though he (or she) slows at a similar rate to others of his age, he has the advantage of starting from a faster base (i.e.--a 13 minute 5K runner who loses 2 minutes is still a 15 minute 40-year-old, while a 15 minute open runner slowing the same amount will end up at 17+ minutes).
A runner who was average as an open runner yet excels in the category of longevity also does well as a masters runner. I ran 14:38 for 5K when I was 24. I ran 14:45 when I was 45.
Coglan was a runner who excelled both in base ability and longevity. That's why he's the only masters runner to break 4 minutes.
Other runners like Coglan will come along, and one of them will undoubtedly break 4 minutes as a 45-year-old.
As for 50? ... Maybe if El G has the longevity ... But definitely not in the very near future (let's try for 4:20 first!).