Verzbicas does not count as he was not a US citizen. My guess is that there have been several Australian, African, and British 18-year-olds that have broken 4:00 over the last 60 years (I know Steve Cram did), so Lukas Verzbicas does not count.
Maton does not count as he was 19. Full stop. Again, lots of 19-year-olds have broken 4:00 and we don't count them. He also did not run any kind of HS schedule. Doesn't count.
Hunter has only broken it indoors. Indoors does not count.
So, one way to look at it is that 4 did it in the last 2 years. Another way is that ONLY TWO guys have done it in the last 15 years ... Slagowski and Fisher.
Hardly a huge trend.
I am sure that Hunter has the ability to do it, but his indoor races just went to show how much faster the 200m banked tracks can be. Last week he ran a 3:42.5 against pros, instead of a 3:57y that was fairly easily accomplished. Again, I understand that he is capable of 3:55 or 56 or 57 but he didn't rip one off yet with ease (like he did indoors).
There was a 4:01 mile in 1965 (Lindgren) and a 4:02 or 4:03 nearly every year for 34 years until Webb, but it did not become commonplace then, and it won't now. To suggest that it will happen every year is stupid.