Github doesn't mean much to me since they're probably working locally and intend to make large commits. As for waiting, they already have a testnet, so I imagine the public alpha will just be a less buggy version of what they have.
Yes you are right, SHIFT dev team is working on a private repo, they will release the code as soon as they finished because there're many projects outthere trying to implement something on IPFS and they do not want a bad competition that steals all the work done