Indeed, but it is critical to me (and I think I'm not the only one in academia for which it is so) that it uses the arXiv funding model -- donations to be susta

Indeed, but it is critical to me (and I think I'm not the only one in academia for which it is so) that it uses the arXiv funding model -- donations to be sustainable -- and not the Github/Authorea model, where you pay for each private paper/repository you set up. --- It is interesting to note that as a programmer, I do not have that many issues with releasing partial or incomplete source code on Github, whereas as a computer scientist, I do not like to release partial or incomplete proofs at all. It might be because the academic community cares about reputation: if you get a reputation as a researcher that releases incorrect proofs, your career is over. In programming, as the names are attached to project much more loosely, such negative reputation is rare and people care much less.