Sorry to respond over three weeks later, but I have two relevant things nobody even touched on:
First, the reason I'm researching bi-directional sync between GitHub and GitLab is that Microsoft already locked me out of one of my previous accounts. Specifically, I can't access my old Hotmail account because I have no SMS number to add to it.
If I set up bi-directional sync between GitHub and GitLab, I can continue to use GitHub-specific stuff if necessary but, if I get locked out by Microsoft for lack of a smartphone, I can push an update to README.md or README.rst on GitLab saying that the GitHub side is a deprecated mirror and have it added to the GitHub repo despite my being locked out from direct modification.
Any one self hosting?
I have been self hosting my own repos from the start, so now I don't have to move anything
If anyone else is interested in self hosting there own, try Gogs, unlike git-labs it has the github style interface!
https://gogs.io/
Self-hosting is generally a bad idea. You have no idea how many times I've been frustrated to find that old Pascal resources I want to for writing utilities for my retro-hobby PC have fallen off the web because the site were they were hosted is gone and the Wayback Machine hadn't gotten around to archiving them. Git as opposed to bog-standard files on an HTTP site will just make that loss of history worse. (If the Wayback Machine doesn't archive something as significant to the late 90s and early 2000s as its FTP sites, I seriously doubt it's going to archive git repositories.)
Likewise, according to the DejaNews archive Google Groups began with, Plug-ins for Program Manager by Plannet Crafters got freeware'd before they went out of business, but it wasn't Archive'd before the site went away, so all I have access to are the shareware versions from various shovelware CDs.
Sure, my blog is self-hosted, but I've been prioritizing preventing URL breakage, so I'm running the same WordPress configuration I originally chose back in 2004. When I find time to take another shot at reverse-engineering the index format for
Sphinx's JavaScript-based site search (to avoid adding a dependency on Google CSE) and write the tooling to verify 0% link breakage and catch incompatible syntax extensions in posts, I want to migrate from WordPress to a static site engine to avoid having to babysit security updates. In doing so, I'd originally planned to also switch away from self-hosting by moving it to GitHub Pages.