To add onto this, I have been using Libreoffice Online or Collabora Online for the last 4 years or so. I used to compile LOOL myself but eventually I just switched over to using the Collabora Online Development Edition that Collabora releases. I am using it integrated with Nextcloud.
I enjoy using it and it has been a life savior for the times I need to work on a document with someone else since I can just send them a share link for it. The fact that it uses leaflet which is meant for maps does mean that the latency to the server matters quite a lot to experience but I don't mind that much, personally, with my not great 120ms RTT to my server.
Element's primary paid service is Element Matrix Services [1] which is exactly for that. They run a Matrix server for you, optionally on a domain that you provide.
A change in your repo does not need to result in an import path change if you set up vanity URLs for your import path. For instance, all my go libraries use the import path of gomod.garykim.dev even though the repos are actually hosted on GitHub. That means if I ever change to self-hosting, for example, I just need to update some of the meta tags on the gomod.garykim.dev website to change the repo location.
I've been running a Matrix server for a half a year and I have not run into any problems. The main thing that surprised me was how much database space Synapse took on my server but that was an easy enough issue to deal with. That may also have to do with the fact that I'm in some of the most complex rooms that exist on Matrix.
I tried running a XMPP server for a bit but that was a rather frustrating experience between getting it to integrate well with the rest of my infrastructure, figuring out what configuration was needed and what XEPs were needed, what clients had the features I needed, what clients supported the OSes I used, and spam. To be fair, the reason I thought setting up Synapse was extremely easy may have been because I did it with almost twice as much experience with devops than I had when I tried to setup the XMPP server.
Regarding registering with a central authority, you're probably thinking of identity servers. Identity servers are used to provide 3PID (email/phone number) -> Matrix ID mappings and are completely optional. There have been attempts to decentralize that as well but for one reason or another, no good way to do it has been found. At least the source code of the identity server is open source[1] so there is that.
Otherwise, to set up a Matrix server, you simply have to either set up a json response from "/.well-known/matrix/server" or an SRV record on DNS that points to the Matrix server.
I don't know how I would live without that. I tend to make rather verbose branch names and typing it all out stuff like push would take forever.
Though, you have a much more fun solution.