I love Lagat, but he's at the end of his career, and time-trialing is not his speciality. Bolota Asmeron is a tough runner and I have a lot of respect for him, but he won't be challenging 13 minutes. Familigetti is a fool (not because he has suddenly taken a liking for showy, Hayward Field front running - there are many more reasons) and I won't include him in serious dicussion.
I think if you look at the rest of the American 5k corps right now, you've got two basic categories:
Guys who are "there"
Tegenkamp
Solinsky
Rupp
Guys who are getting "there" and will be "there"
Jager
Fernandez
Derrick
In my opinion, all six of these guys have the genetic potential to break 13 minutes. Jager, Derrick, and Fernandez (who are 20, 19, and 18 if I am correct) have put up outstanding times for runners their age and if they stay healthy, I don't see why they shouldn't threaten 13 minutes.
Yet things always happen. It's a long shot, but does anyone really see six Americans going under 13 in the next few years?
If they got in a fast race either this summer or next, Solinsky, Rupp, and Tegenkamp could all come mighty close to 13:00. I hate to say it (only cause I'm a huge Solinsky fan), but Rupp is probably the more likely to do this.
My predictions for PR's the next two summers:
Rupp 13:00
Solinsky 13:02
Tegenkamp 13:02
Jager 13:08
Fernandez 13:12
Derrick 13:12
It's so hard to predict the younger guys. I mean, Derrick and Fernandez could still grow (as in height/weight, etc).