We can speculate at that but we can also speculate that his lifetime best, set in 1994, is likely not representative of the ability he had when he was dominating the 800m. When you're running well in the 800m, sometimes you can get into a 1500m or mile and really hit it, as Krummenacker did in 2002.
Rudisha has yet to run a 1500m but he could probably run a decent one, if his training partners give any indication.
Alysia's a very talented young woman, and though I'm not privy to the details of her program, she does train some with the BATC.
I think Pamela's husband/coach has done the best he can to ensure that she never returns to her 2008 ability again.
Phoebe's 1500m best is 4:15.66 and, taken together with her 400m best of 53.79 (set four weeks after her 1500m personal best) is right along the lines of other J.J. Clark athletes (all of Phoebe's PBs are within half a second of Hazel's).
Maria Mutola for one. The list is short, to be sure, because you have 52.0 speed (or better, in Maria's case) you're probably more likely to try your hat at being a 400m or 400m Hurdles specialist.