Yep, I don't want to host the API myself but I want to know it's possible should the need arise, ala self-hosted Gitlab.

Well, it has got some real time data syncing stuff going on (which gives it Google Docs capabilities), I don't think that is trivial to do yourself.

I meant specifically when building a CMS. Being able to build a CMS that is multilingual, that can adapt to any form of content and workflow + be easy to use for editors is much harder than implementing the underlying technology.

Yeah, sorry for misreading you. That's indeed a good point (although both things are hard ^^_).