All the issue/PR discussions and CI/CD are the real problems, and this doesn’t seem to help at all, so good luck collaborating without changing your workflow when GitHub is down.
But yes, if GitHub is down, then your workflow is going to change. We're hoping to close that gap down the road, but having a way to continue pushing and pulling with collaborators with a very quick setup seemed compelling to us. Not to mention the benefits that decentralization itself brings.
The vast majority of git users tend to agree on one "origin" remote and 99-100% of their pushes and pulls are to/from that remote. So git, in practice, tends to be centralized when it comes time to collaborate with others. We're trying to re-decentralize that aspect while accommodating the convenient workflows we're all used to.
I think a counter to that is only one person needs to set up the additional git remote, compared to everyone having to install additional software to use dgit.