From the announcement thread.
Calls to enableModules and disableModules seem to be missing for some features at other than install/upgrade time.
I only see calls for calendar and drafts.
I do not see calls for mentions and attachments and know for certain enabling attachments doesn't work. I did not look to see what other modules exist that do not get enabled or disabled.
I did already track it at https://github.com/elkarte/Elkarte/issues/3016 this afternoon based on the other report. :)