We do not publish roadmaps for the product. Posting in here is the correct thing to do, and if things like this are to be added, you would see them appear in blogs
As mentioned there is no webhook for member tagging at present, unfortunately. Please feel free to post this up within our feedback forum if it is something you would like to see in a future release
Within each forums settings, on the first tab, you have "Users can see topics posted by other users?". But this would apply to everyone other than staff
There is no way in which to do this within the system at present unfortunately. You would need to get them to add themselves, or as you mentioned, log in as them to do so