I came up with a neat Uncharted 3 idea during my 4th playthrough while in the ice caves.. I'll leave the details of the adventure to the pros but here's what I have:
Remember all the remains of Shafer's expedition? The ropes, boxes, ladder bridges etc? Well what if the new game tasked Drake with setting up his own expedition? How cool would that be having to actually figure out a way across gaps and up walls without stuff already conveniently available? I think this would take away some of the linearity issues some people have with the game.
I also see co-op working very well here. Let's say a bridge needs to be made to get the equipment across a gap. Person A climbs some ledges and gets to a higher point where he lowers a rope for person B with light equipment (can't climb ledges). While up there, person A creates a rope swing to get across this shorter gap. Person B now must throw the equipment to person A across that gap. This could be a fun mini-game where timing and accuracy is key. Person C waits behind to construct the first half of the bridge while persons A and B across the gap construct the other end of the bridge. I picture those rooftop bridges from UC2 but 2 needed to meet in the middle. Now if this were a 4 player co-op game, I can see 2 shooters, one on each side, needing to defend the builders from an enemy ambush. To balance things out and make it fun for all players, I imagine having the bridge builder injured causing the shooter to take over while the injured player rests against a rock with a gun needing to defend his buddy .
That's just one scenario of many that I've thought of.
People want to see Tenzin back and the only way I see that happening is if Drake was tasked to lead an expedition and hiring those he's worked with and trusted in the past. Imagine seeing Drake, Sully, Elena, Chloe, Tenzin and possibly new characters plus the random human mules carrying equipment all making their way through some tombs together... fucking awesome. I also see Eddy and Rika's return as they have their own team assembled. Eddy has a giant scar on his neck and Drake of course questions why he's working with his sister because they both know what happened in the past (Eye of Indra for those who don't know). I see the teams joining together after some animosity because they are both losing people fast. BUT, something terrible happens and Eddy is trapped while everyone is forced to exit the tomb until later when they finally rescue Eddy. Here's the kicker.... DLC! Uncharteed: Eddy's escape. Yeah, i went there. You play as Eddy from the time he's trapped to when he's rescued to see what has happened during that time period as well as the discoveries he has made which answers questions of why Eddy acted a certain way at the end of the game.
It's hard putting this stuff into words but my job allows me the time to think of this stuff and I love it. ND, if GAF approves, I don't mind if you steal my idea at all.