Hello Joel,
Since there seems to be interest from GSOC students who want to work on converting builtins, I figured I should finish what I have that works now so they could build on top of it.
First of all, I must thank you for submitting this series of patches. It is a great starting point to convert 'git stash'.
I would like to continue your work on "git stash" if that is fine with you. I will continue to build on top of it, starting with applying some patches in order to implement what was already suggested in this thread. During the summer, I am planning to finish this process and, hopefully, have a 100% C, built-in 'git stash'.
Best regards, Paul