That external LCD display is nice (and cheaper than a G15), but still poses the problem of everyone not having one or willing to pay for it.
As far as steam replacing Vent/TS, I don't ever see that happening. Maybe if you only talk to a few people, but when you have guilds of 20-40, VoIP on a regular connection would lag terribly.
I checked out GameOverlay a long time ago. It was decent, but 1) wasn't free, and 2) it was just overlayed images, you couldn't interact with them. And overlaying something large like IE or iTunes would probably drops your FPS alot.
It would be awesome to see Blizzard put IM/MediaPlayer/Web integration into WoW. I don't think anyone would ever leave the game then haha. There's already a few addons for music (
MusicPlayer ,
SimpleMp3 Player). Or you could just use a tool I've already made (
HotKey Mapper) that controls your favorite media player while it's in the background. This way you don't have to move your files around or make new playlists.
I think the solution I'm going to try for with the AIM/MSN problem is an Xfire style overlay, but just have it interact with IM windows in the background. The last thing anyone needs is another chat client