Uncharted 4 will be a GF rental for me. I feel little need to jump back into those games after I've beaten them once. Still, you never know as far as MP goes. Maybe they could make it not suck.
Here's a review of the MP test they did back in December. Looks like it's not just a simple tacked on MP.
I know that people liked the multiplayer in Uncharted 3 and The Last of Us. It's not that I think it will suck. It will probably be okay but if I'm going to play a multiplayer shooter I'd rather spend my time on games like COD, Battlefield, Battlefront, Titanfall, Halo, CS:GO, or Gears. Those games all make multiplayer a major focus where it's more of an additional option in Uncharted.