Would you consider a feature to have the dashboard site treated as a child site automatically? It seems this might be a nice idea for new users who don’t necessarily think about the need to keep their main dashboard up to date (and secured with security plugins). My thought here is that your child sites are only as secure as your weakest link, and if the dashboard is neglected this can be a serious issue.
For example, I have extensive security plugins installed on my child sites, but I just set up a fresh MainWP dashboard and hooked it up to these child sites, but I haven’t yet installed all the security plugins on my dashboard site. Therefore, my child sites are now unprotected if a hacker knows my dashboard site URL and is able to get in due to the lack of security plugins in the current state.