Google storage has worked using the same sort of API since it existed. In-fact using googles sync tool for your S3 buckets is significantly faster (last we tested anyway, we have since moved to Google cloud as it is cheaper and faster).
I don’t understand how discourse still only supports S3. Since google buckets use the same API hopefully I can hack it in but jesus… the fact I found a thread from 2014 asking for simple backups to something other than S3 and it is still not provided (or even mentioned). Should have just said “no” instead of pretending it might happen. This thread further shows you haven’t even thought about anything but S3 since you never even knew other services have compatible apis…
So hard finding any information about discourse too. Just links to threads with out of date information. Just glanced at github, issues not even enabled (I assume to try force people to post on your forums, this is just a barrier to entry for developers, the people who would contribute to an open source project).
Every time I have to do something with discourse I just run into issues because of weird philosophies, lack of information or because the original setup we have is bad (multisite). Trying to properly setup everything now with separate servers for postgres, redis and each forum and naturally I don’t want to have files on the app servers (this is a very outdated way of handling uploads) and you provide a single (bad) option instead of it.