Many other forum softwares and forums I have used before have a Blizzard style quote for use in quoting patch notes, or dev responses, etc. I'd really like to implement that into my forums, but do not see it anywhere on here.
I'd be very much interested in this as well. Editing the css itself is not such a real daunting task for the message body, but making it costumizable for people who don't know css might actually be a very nice idea for an addon.
Also the problem starts becoming when someone 'non blue' is quoting a blue, which could override the styling. There's an entry in the xenforo manual that might help you further with this https://xenforo.com/help/user-group-styling/