It would be very helpful to me to know when my friends were last online. Having something at the bottom of the inspect window with a "Last Seen: ___ Minutes/Hours/Days ago" would be nice. If it goes into months, I would be happy with "Last Seen: Long Ago." And leave it at that.
The major utility I see in this is coordinating with friends, and knowing if I missed them or vise versa. Knowing if I should wait for them without using third party applications like discord isn't currently in the game. It would also be nice to leave a message for offline friends like "Out for the night" "Gone fishing" "Be right back!" or "Crashed Out" that can be set upon logout from the account. Of course, I want to see "Crashed Out" be specifically for when the game closes with no opportunity for a message to be selected, and a no message option to leave the message field blank.
All in all, I want it to be easier to coordinate with my friends when we aren't online.
I absolutely LOVE the idea of adding in little messages for when we log out. Unless in a questing mood for a specific character, I typically switch between all my characters every couple minutes to do minor things/trade things in shared bank/etc. It would be super nice to be able to add a little message to tell my friends on one wizard that I'm on another wizard and will be back. And ESPECIALLY the crashed message is great (especially with how much the game has been crashing lately due to the influx of players). Hope to see this implemented!