Ever since GW2 had set itself up for a story where the heroes would have to go on a long journey to defeat the six dragons, I was worried that the game might not run long enough to see the conclusion of that story. It doesn't help that they inflated the the story between each Elder Dragon arc, with Scarlet before Mordremoth and Balthazar before Kralkatorik. We're three paid box games and four seasons into GW2, and only two of the six big bads are down. Unless the writers start having the dragons devour each other to lower the number of dragons we need to kill, pull out some sort of superpower for the heroes to start downing dragons very quickly, or otherwise skip the box set/season long build up to a dragon fight, I don't see how Anet can satisfyingly resolve the GW2 story before the plug is pulled.
I really, really want to see an underwater/naval expansion against the last and most dangerous big bad of them all, the Deep Sea Dragon. There is so much potential there!