Yes, it's possible to create various limitations, approvals, etc... just making a point that @mentions is a seemingly trivial issue, but it carries a whole bunch of considerations and extra settings. We'll get to it anyway. :) It's needed.

We really don't want to make our own WYSIWYG editor :) ... we did it back when we built early versions of Orca forum, but it was a mess. We plan on using Froala editor in the future, but generally, UNA can work with different editors. 

I now understand you about the messenger notification link issue. Thanks!