I do not think that this is going to happen because naughty dog confirmed that the last of us will already have multiplayer so there is no need to add its characters to uncharted 3 multiplayer. Besides Naughty dog is not going to add any game characters that do not have a relation with uncharted series to U3 multiplayer.
I understand you and I see what you mean. Yeah sure Naughty dog had released before killzone skin dlc for uncharted 3 and they added the capture trooper from killzone to uncharted 3 multiplayer but it is just that I have a feeling that naughty dog might stop doing this in the future and that naughty dog might not do this for the last of us but it is just a personal feeling so yeah naughty dog may or may not add last of us characters to uncharted 3 multiplayer, Who knows? but overall I support your idea and I would be glad if they add them to the multiplayer.
let me guess the jobless bums tripleWRECK, DAI, PDISS, and brad badewood will all quit everything they are doing in life and practice 10 hours and day and play on one big team and ruin the game for randomsand non hand holders who want to just have fun.. no thanks