Although it is not very painful to convert an existing repository from hg to git or viceversa, using hg-fast-export for example, the issue of preserving users, wiki and issues tracker still remains.

It would be very useful, given that you offer more than just a repo, to have that hg-git switch implemented.

Maybe you can even consider maintaining dual repos and synchronizing them, so everyone can access them using both hg or git. Just thinking aloud, I don't know if that is even possible, but it would surely be a nice feature.