Well, then we should create open-source analog of notion. I actually was itching wondering what could I create in OSS realm. Probably will have a look at this task :)
stackedit.io has been the closest that I could find.
https://news.ycombinator.com/item?id=18906118
Haven't tried it out personally (only support signing in from Slack/Google), but it might be your kind of thing. :)