I think keeping @Mods being @Mods instead of including all 5, 10, 15 members of the ‘Mods’ group with their own individual @s seems like a great space saving suggestion.
I could see some practical uses for this as long as the UI keeps a means of restricting who can reference specific @'s.
To follow your example of
Hey, I have this really cool idea. @mods what do you think?
Ugh, allowing people to reference staff because of an ‘idea’ on a large forum would be the stuff made of nightmares. Everyone thinks they have a ‘killer’ idea and the @mods or whoever will simply get in the habit of ignoring the notices due to the frequency of them. In these situations, encouraging users to post ideas in a suggestion forum is a far wiser idea.
Now, allowing certain groups the ability to reference groups sounds like a great means of providing an escalation process.