I'm actually pretty tired with all those games that try to force co-op into the main campaign. It's just not plausible to see two main characters every time. That said, four or so characters could work in a war game or something similar very well.

Yeah, if it works with the story, I'm all for it, otherwise no.

No coop, this is one very, very rare shooter that coop is not a must. CoD:MW2 , Killzone 2, and Resistance 2 all would be way better if they were, but this game was so danm good. 

Split screen coop and competitive multiplayer online and offline. Also increase the multiplayer count by 2.

No.  The last thing Uncharted needs is a brain dead AI partner when not playing with another person (I'm looking at you Resident Evil 5).  I personally hope the third game is a little less shooter and a little more adventure.  So that in itself would not lend to a co-op story mode.

I want split screen co-op but I don't want an AI in place if I play single player.  I want it like Halo CE, you just have a clone of the main character.  I find many games much more fun playing split screen with friend.  There's nothing wrong with adding a co-op option.

But with Uncharted being so story driven, random cloning and playing popping will be out of place.

It was out of place in Halo as well but it was nice to have the option.  I just think it would be a good comprimise, the single player stays intact and remains a story driven adventure, but now you can enjoy it with a friend.  Leave all the cutscenes and such as is and make it seem like the second player doesn't actually exist. 

That takes away from the immersion of the game.

I agree, but you don't have to play it that way, it's just an option.  Like it or not, there are many people out there that want co-op, and I think using a clone is a good comprimise.  The gameplay stays in tact and you get another option.  I like options in games, even if they're useless to me.