I'd love to see a game based on the adventures of Drake's son or something based on Sully in his youth.
I'm fine with stories ending. It's so easy to fall back on a popular brand because dem monies doe, but I don't like it when stories are stretched just for the sake of the name brand. Case in point, Gears of War.
I would love to learn more about Sully and play a game based on his early exploits. If Drake has a grandson, maybe even a story based around him finding out about his grandfather's adventures and setting off on his own.
I'm all for more Uncharted games. That's a franchise teeming with compelling characters and I trust Naughty Dog has plenty of more spinoff ideas brewing should they decide to go back to the well.
As much as I adore the series, I have to agree with everyone else. I'm open to the idea of exploring new characters but not at the cost of the series losing its luster. Maybe ending Uncharted will make room for a fresh IP! I've seen some suggestions of Naughty Dog handing over the series to another studio. I'm a little apprehensive about that.