Come now, sir. The point of the exercise is the challenge. I challenge you to prognosticate.
How about this? Surely the future world mile record will be hard pressed to beat even the current world 40 yard dash record times a factor of 44 (40 yards x 44 = 1,760 yards = 5,280 feet). So what is the current world 40 yard dash record?
And when will we get there? 2010? 2090?
Technically, I'm not required to respond to this challenge, since it wasn't posted in the comments to the original challenge post. Being an accommodating pundit, however, I will entertain the question:
The 40 yard dash is not a track and field event, but a tool used by collegiate and NFL scouts for recruiting purposes. A football player who has a time in the "40" that is over 4.6 seconds (hand-timed) is usually not considered for any of the "skill" positions: quarterback, running back, wide-receiver, and defensive back. Therefore, official records are not kept, since it is not an event. Still, the fastest time ever recorded electronically (hand-timed races, due to human reaction times, are usually 0.2 seconds lower than electronically-timed races) is a 4.21 that was run by Maurice Greene en route to a 100m time of 9.81 seconds. Let's use that time for our purposes here.
If we multiply 4.21 by 44, we come up with a time of 185.4, or 3:05.4. Can a human being ever run a time of 3:05.4 in the mile run? I'd say the chances of that are less than of the Pundit running a 4.4 "40" or a sub 4:00 mile, and neither one of those are ever gonna happen! Could it be done with genetic engineering? Possibly.
Okay, I don't like doing this because it's for posterity (and posterity usually makes dunces of critics and prognosticators) but I'm going to say a sub 4:00 mile is possible for women by 2057. Using that standard as a meter stick (women improving by at least another 12.56 seconds) men also should be able to improve by 12.56. That would put the world record for the mile at 3:30.57. I think a time like that would be possible by 2057. What will allow for these improvements? Better training techniques will be discovered (the Lydiard Method is 47 years old as of this writing), better technology (shoes, physiological monitors, uniforms, track surfaces) will be developed, the nutritional aspects of running will be further explored, psychology could be used to increase our threshold of pain, genetic "pockets" (such as those good folks in the Great Rift Valley in Kenya) will be discovered that are ideal for mile running.
After that? Genetic engineering would have to be explored to further improve times and I don't think the IAAF is prepared to deal with the thought of Übermensch. Right now, they can't even deal with the thought of a legless man competing in the Olympics.