RFD: a submodule-like facility that tracks branches rather than commits

Has consideration ever been given to a submodule-like facility where
the configuration information maintained in the supermodule for the
submodule is not a gitlink but is instead the name of a branch (or
generally, a symbolic reference within the nested submodule).

In this case, "git submodule update" would checkout the specified
branch of each submodule rather than the specified commit.

Of course, the intent of such a facility would be to allow git
supermodules to be used to simplify management of a group of related,
yet indOfependent, git projects.

jon.