A decentralized GitHub strikes me as a really good idea:
First, the practical reasons: GitHub might become untrustworthy, get hacked — or get DDOS’d by China, as happened while I was working on this project! I know GitHub seems to be doing many things right at the moment, but there often comes a point at which companies that have raised $100M in Venture Capital funding start making decisions that their users would strongly prefer them not to.
There are philosophical reasons, too: GitHub is closed source, so we can’t make it better ourselves. Mako Hill has an essay called Free Software Needs Free Tools, which describes the problems with depending on proprietary software to produce free software, and I think he’s right. To look at it another way: the experience of our collaboration around open source projects is currently being defined by the unmodifiable tools that GitHub has decided that we should use.
I continue to find it rather amusing that so many people who complain about Google and other companies like it being evil and untrustworthy (not necessarily an incorrect claim) will happily bake GitHub into their development and release pipeline. Even assuming GitHub is staffed top to bottom with honest and well-intentioned people, it is still a bad idea for any number of reasons.