A few of my teammates had this debate during a track meet yesterday.
Let's say you were given 4 random non-disabled guys in their 20s and had to form a 4x200 team using only those guys. Could they be trained to break 1:40.9 within a year? You're probably going to get a no-talent that can only manage a 27, but would that be balanced out by the studs who can run a 23? Three of the guys have running starts, so this seems at least somewhat plausible.
BTW, we chose the 4x200 because it seems like the most realistic relay squad for this concept. There's no way you could get a random 4x100 team to beat van Niekerk's 43.03 time, and the obese guy(s) on the team will kill the 4x400 squad's shot at beating El G's 3:43 mile time.