I am actually satisfied with this approach, and it seems reliable.

>
> As you suggested earlier, maybe we need to modify vc.el, making the restriction looser? 

If you can, try out the above patch and tell me if you end up having any
issues, otherwise I don't think we need to adjust vc.

> Also, I noticed that the maintainer bind `default-directory' in this commit: 
>
> https://github.com/emacs-mirror/emacs/commit/7ab556b57631cb28db86b89ba296bc0599d9a399 
> Improve robustness of 'package-vc-update' Regards

FYI that was my change, GitHub just doesn't display commit names by
default:

https://github.com/emacs-mirror/emacs/commit/7ab556b57631cb28db86b89ba296bc0599d9a399.patch

-- 
	Philip Kaludercic on peregrine