I like that idea if the floating bar if its small. If it starts taking up real-estate of the screen it might interfere some. Testing it out could be interesting.
I know you're working on the notification and I'm sure its super complicated. Do you think one step in that direction could be as follows...
Currently we have 2 boxes of missed notifications.
Unread posts and Private messages
Do you think a third box could be added that says tagged post ( if someone tags you in a post @falcon)? I know an email can be setup to contact your but being within seems like a great function.
Cheers