You say that, but it is very telling that every large company out there (Google and Facebook come to mind) go for the single-repository approach.
I'm sure that, when dealing with stakeholder structures where different organizations can depend on different bits and pieces, having multiple repositories with difficulty of making breaking and cross-cutting changes, becomes good.
From the view of a single organization where the only users of a component are other components in the same organization, it seems like there is consensus around single-repository.
"Best guess" can be bad if it is not well-defined, but you can still make error detection obvious rather than hidden.