"bonus mission packs".
The studio is "open to whatever" fans want in terms of more content. It could arrive as DLC or as future expansions - all of it is "yet to be determined".
"...after reading the PC Gamer article I wanted to make sure that we clarified a few things. First, we haven’t decided on what exactly we are or aren’t going to offer for money post release. My answer to the dungeons question was meant to say “we’re open to whatever our players seem most interested in,” ArenaNet.
"If after release you guys would like more story content, more dungeons, more events, more maps or whatever it’s something that we have to consider because ultimately making you happy is what makes us successful."
"Whether we release that in DLC (like the bonus mission packs in GW1) or whether we do it through expansions (Like Eye of the North) is yet to be determined," they added.
"As to whether or not there are going to be items like XP boosts available in the in game store I can only reiterate what we’ve said before (and will continue to say) that we’ll release details on it when they are available and that our core philosophy--of not requiring you to spend additional money to play the game and not making the game difficult or painful to play in order to encourage you to buy things from the store--still stands."
All this summarises too: no decision is made on whether to charge for additional dungeon content or not. Guild Wars 2 is a free-to-play MMO just like the original and is due for release next year. ArenaNet have been slowing unveiling more of the game.