Look: I don't think there'll be Will's son in the next film (if there is one, which there probably will be). And in addition, there's enough stuff set in place for a new one, Johnny Depp's all for it, Keira and Orlando don't want to do it - and that's great, Will and Elizabeth's story has been put in a way where it can either be done or not done - we have a new story we can lead into, we have an enemy - and more additional enemies (PotC: AWE video game showed Black Bart), and much more, enough to make a 4th movie - and possibly a 5th...
I'm in love with the franchise, so I don't really care how many more they make - one, two, a hundred... but my one thing is that it HAS to have Jack in it, and only Johnny can play Jack. Otherwise it's going to suck. Seriously.
Hah, I'm such a pirate nerd... and proud of it ;D