Drugs or not, El G, Komen, Bekele, Gebreselassie, etc. were once in a generation talents. That's why no one has broken their world records, because nobody since these men have been good enough.
Kiprop has a very good shot at breaking 3:26 and 3:43, however I don't think he'll ever surpass El G's record of 31 sub-3:30 performances. El G dominated the world at 1500m like Bernard Lagat dominates americans at 5000m.
Isiah Koech and Hago Gebrihiwet(?), assuming they both really are just 19, also have a chance to develope and improve, but even then they are still 10 seconds away from 12:37.35. But remember when Eliud Kipchoge ran 12:46.53 in 2004? He was only like 19 then, and he never broke 12:50 again. Basically, Koech and Gebrihiwet could follow 2 paths, and I certainly hope they don't follow the former.
The 10,000m record will likely take longer to break than the 5000m record because it will probably be someone who is really good at 5000m who is also a good 10,000m runner.
3000m record is practically set in stone, so we best get used to that.