Hello,
It seems that most of the currently scripted commands can't be implemented with libgit2 as it's still not mature enough to handle it (eg the whole merge part is still missing), though we might have missed something.
Thus we've chosen to first focus on two simple plumbings: commit-tree and cat-file as there is the material for it in libgit2 and the command signature is restricted to only a few parameters. When it's done, we'll try to compare the efficiency of this partial port (works well and quickly). Thanks to that background, it might be easier to move on other plumbings.
Romain Geissler
(Sorry for answering you directly, i should have checked the mail recipient before sending it !)