This is great news! I've always had my repositories spread across GitHub, gitlab, and bitbucket depending on what size group or features I needed but this helps centralize everything to GitHub. That is probably their goal!
Oh dear. That doesn't really sound like a good idea in the long term.
So once you place all your projects/repositories on a third party git service like Github and it goes down, what can you do to push that critical change? Might be no big deal for personal projects but unacceptable for big business and open source orgs.
You might as well call the CEO of GitHub for support. A better way is to self-host...
Even ignoring the higher cost to set up, are you sure your self-hosted solution will have better uptime? Are you sure you'll be able to get things up and running faster when it does go down than GitHub will when GitHub goes down?
Why you ask? You have total control over the stack, CI, etc and some orgs have in-house sys-admins or IT department to do all the work independent of a third party like GitHub. Maybe you should ask the Linux Kernel Project, WebKit, OpenBSD, Mozilla Firefox and even RedoxOS maintainers about why they self-host their projects which some even have mirrors on GitHub.
On another note I keep seeing this over on some repositories and now because it is 'private' I don't even think it remotely makes sense or is a good idea to even use GitHub to backup private keys even if the repository is 'private'. As long as it is on someone else's server, you're not in control.