I'm not sure this has been mentioned or not, but I think a healthy Ngeny could have given it a run. The video of his 1000 record would make your jaw drop. Unfortunately we'll probably never know.
It seems a lot of the discussion is for bumping a sprinter up, when I think realistically sub 140 will come from some Ethiopian or Kenyan with great aerobic background who just decides to sprout some wheels.
Also, which comes first...sub 140 or sub 340?