I had an idea to add something to the social tab to indicate that you are Away From Keyboard. If you can turn on the setting in the social tab, it would let all of your friends know that you aren't able to respond to PM's. This could also serve well in case you are muted.

Example: (Just using Apollo as an example)


*Or*


Indicating that Apollo is unavailable to respond to PM's.


This could also be included in the guild tab as well.