> It is because it hides the particular detail about the format we use.
As the function I added it's internal and just used from describe-mode, I don't think leaking that detail is something to worry about. In fact, you can un-leak it just by renaming the function to help--docstring-without-usage ;-)
> Indeed, to do that we need to see how it's used to see whether it can
> safely be changed as-is or whether it needs to depend on some new arg
> or something.
Of course. Easy to do for our uses of help-split-fundoc, and I'm willing to do it. But we don't know if and how it is used elsewhere. There are a few uses already in ELPA, for example.