According to the ever-vigilant Team Fortress 2 forumites who take great pleasure in dissecting anything and everything to do with the game's code, there's an amusing MMO reference in the last patch.
The following "code" was unearthed in the game's GFC files:
// TF2 MMOAmusing, yes; a sign of anything other than riding the community's ability to read into things that aren't there? No. Still we thought it was funny.
"TF_MMO_LFG" "Looking For Group"
"TF_MMO_Quest1" "You must kill %s1 %s2 to complete this quest."
"TF_MMO_Monster1" "Boars"
"TF_MMO_Monster2" "Rats"
"TF_MMO_Monster3" "Bats"
"TF_MMO_Monster4" "Wolves"
"TF_MMO_Monster5" "Spiders"

DING!


Guess I'll just have to make do with aiding those Heavies with my mad Medic skillz.