I just looked at the Olympic schedules for the men's track events, and most of the common doubles are planned for:
100-200
200-400
1500-5000
50000-10000
steeple-50000
doubles which are essentially impossible:
400-800
400h-400
800-1500
1500-steeple (not that anyone ever tries this anyway)
I'm noticing some bias. It seems Coe doesn't want someone else to try what he did.