When posting a comment I don't know who will receive the update and I need to include all users to ensure they receive my update. It would be helpful to see the list of users who will receive the update.
In addition, identify users who have PTO (either in red or with PTO in their name. Allow the user to toggle PTO on their account (if they do not use the PTO system) so they can toggle on or off before they leave and after they come back.
We just deployed to a new team and having to explain to them that there really isn't a way to tell in a single place who got the message is plain embarrassing. The message will go to the people tagged, so we look at the little people icon, the people subscribed (need to look at a different hover icon), the primary contact, the assignee, maybe even people subscribed to the project?