I got a helpful response to the following question almost 5 years ago:

On 12 November 2012 at 23:09, Adam Spiers [off-list ref] wrote:

On Mon, Nov 12, 2012 at 6:18 PM, Drew Northup [off-list ref] wrote:

quoted

On Mon, Nov 12, 2012 at 11:37 AM, Adam Spiers [off-list ref] wrote:

quoted

As it turned out to be fairly easy, I was wondering if there would be
any interest in doing this more formally, i.e. splitting off the
framework so that it could be used and improved outside the scope of
git development?  Of course this would pose the question how git would
consume this new project without any risk of destabilisation.  I'm
guessing that simply using a git submodule would solve the problem,
but ICBW ...

Just an idea.  Interesting, or terrible? :)

Done at least once already:

http://comments.gmane.org/gmane.comp.version-control.git/201591

Nice!  So hopefully someone will submit patches to build a two-way bridge
via git subtree.  Having them diverge would be sad.

but sadly since then gmane has shuffled off its mortal coil and I can't
remember / find what this URL referred to.  Please could someone
point me at a working link?

Many thanks!
Adam