Hello,
Rune Would it be possible to have a chatgroup to replace messaging apps like WA?
Many services and open source projects already exists, offering chat group functionalities. The best one for your privacy is Signal.
We don't want to compete with them, as they are very good at what they do, already offering an excellent service. Trying to go there would be a waste of time and resources we don't have.
Rune Would it be possible to have people notified (like google docs) when you add a comment to a document?
Regarding external notifications, it's something we have in mind. See the discussion on this GitHub issue: Email notifications #1047.