Yeah, that was supposed to happen in February, according to the Rumor Mine. That's the last time I'll trust Pocket Gamer's rumors!
Too many to name, but off the top of my head. By multiplayer I mean truly online multiplayer. Any game with local only multiplayer needs online multiplayer. NBA Jam Speedball 2 Street Fighter IV
Games that should have mulitplayer: Battleheart Age of Zombies Infinity Blade (the update better be out before April) Games that don't NEED it, but it would be interesting to see how it was implemented: The Blocks Cometh League of Evil Wispin Plants v. Zombies etc. I think 90% of games would benefit from multiplayer, as it honestly can't hurt the game.
Hmm... I'd say: Gangstar Max Adventure Bug Heroes (would be rather interesting with MP) I'm sure there's a ton of other games that would be great with MP.