It can and will be done.
Naturally, when specializing for one distance the speed at the other distances will suffer slightly. For the most part these are the times that are always within several months striking distance of the runner that is able to break 2:00:00 for the Marathon in ideal weather conditions with support of other runners.
If a major marathon created a new team division, a la XC with 4-7 runners per team, but started each team 2-3 minutes apart, the 2:00:00 barrier would fall, especially with a $1M bonus to the winning team. Team Kenya v. Team Ethiopia v. Team Eritrea v. Team Uganda v. Team (rest of world's best runners?)
400M = 48.4
800M = 1:44.6
5000 = 12:57
10^4 = 26:43
Half = 58:12
Full = 1:59:59
With a bodyfat around 4-5%, the mass will most likely be 1% either way of the following.
5'3" 115 lb
5'5" 122 lb
5'7" 130 lb
5'9" 138 lb
5'11 145 lb
6'1" 154 lb