I assume the documentation build process needs sphinx, is that correct? If so it might be easiest to factor out a documentation into a separate python2-kwant-doc package.
Indeed, and that's why we separate the two for Debian as well. There's python-kwant, and python-kwant-doc.
Also, could you please have a look at http://kwant-project.org/install#arch-linux and let me know if something could be improved there?
Yes! I forgot that in my last mail, a notice with which PGP key you make signatures and that this key needs to be added to the keyring of the user building the package would be most helpful.
I don't have any experience with Arch, so it would be most helpful if you could write a few sentences yourself that we could then include into the instructions.