I doubt it makes much sense.
* Things like toplevel and cdup are not even something you
configure. It is where you are, the current state of you.
"git config" does not make any sense at all.
* manpath and execpath and friends _might_ be something you may
want to configure, and teach relevant codepaths to pay attention
to the new configuration values. But until that happens, it does
not make sense to have that information in "git config". "git
config" does not show values that are not actually configured, so
it won't be a replacement for "git --man-path" for those who do
not have nonstandard place configured.
So...