I don't really use Steam - you can probably email NC Support and see if they know, but they might not either. Best bet would be to contact Steam directly.
Manga @ Triumph
"Meanwhile In The Halls Of Titan"...Titan Network Working To Save City Of Heroes
Save Paragon City! Efforts Coordination
Hey, it seems the in-game overlay for Mac will not work, at all. I looked it up, the best I saw was a fix for the PC version, which made it not run the updater, so that when the updater closed it wouldn't think the game closed. This allowed it to actually recognize the real game for well, the real game. So you can actually use it correctly.
So uh, is there a fix for this, or will there ever be one or what?