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 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!
Bryn says: Hah. This is awesome. I love how Valve continues to joke around with its products, while remaining committed to keeping the hardcore on their toes. Don't get me wrong; if there was the slightest hint of a TF2 MMORPG, I'd be the first in line with my smoking minigun to slaugher rats by the hundreds just to hear myself ding.
Guess I'll just have to make do with aiding those heavies with my mad medic skillz.