I understand the basics of the science behind the argument that we won't see a sub 2:00 in our lifetime. It's hard to argue with much of it. But here's the thing...every time the pundits, and I'll include us in that group since we're discussing this from a theoretical perspective, state that something Can't Be Done, or when general thought is that something can't be done, guess what... Someone is determined enough to figure out HOW to get it done. Whether it be sports, or medicine, or man's great achievements, the one commonality they all have is that the prevailing thought was that they couldn't be done. What makes us so smart in 2013 to presume to "know" what man's limits are, or what they will be in 20-30-50 years?
I remember when Dinsamo ran 2:06:50 in April 1988. That set the world record at 4:50/mile, and it dropped the record by 1:15 (~3 seconds/mile) from what it had been 3 1/2 years earlier and by over 2 minutes from what it was 8 years earlier. Dinsamo's record stood for 10 years, and to me it seemed to get to the point where it was a question if anyone could go lower. Had racers hit the limit in the marathon? Then after da Costsa broke Dinsamo's record the record fell another 3 times in 5 years, capped off by Tergat's 2:04:55 which established the record at almost 2 minutes lower than it had stood for 10 years.
So that's 4:53/mile to 4:50/mile to 4:46/mile in 19 years. Over the last decade it has come down another 1:17, another 3 seconds/mile. For whatever reason, call it drugs, call it improved course design, call it whatever, the fact is that TPTB recognize a world record now that was unthinkable 30 years ago. Ask Steve Jones after he ran 2:08:05 in Chicago fall 1984 if he thought someone could run 10 seconds a mile faster and I highly doubt he would have taken the question seriously. Yet he has lived to see the record he set lowered by 4:27.
If someone offered me a bet that we won't see a sub 2:00 in my lifetime (I'm 47) pragmatically I'd take the "not going to happen" line. But like I said above, every time we say something can't be done it's just a matter of time before someone does it. To me, it will happen when the HM record gets down under 57:45 and we see more runners putting up HM times in the 58:30-59:00 range. We've only had runners under 60:00 for HM for 20 years.