It looks interesting as an app, but in context of self-hosting there are couple of speed bumps:
The server side is quite complicated. (compared to Joplin for example) It’s multiple services and it also needs Mongo, Redis and S3. Makes sense for them to do it this way to be able to scale up, but for few users hosted locally it’s quite a lot of moving parts.
You need to compile client apps to self-host. This effectively kills this as an option on iOS.