That's according to
, which caught up with the developers over PAX. No real details are available on exactly what form these will take, thought MMORPG.com reports the plan is "for players to be able to create and host their own servers or games with specific rule-sets". The obvious is for would be arena and PvP matches, but there's no reason it couldn't extend to other modes too.
These servers are unlikely to be player-hosted dedicated servers though, with simply allowing groups to claim and configure an instance much more likely - and while a full on supported modding community would be incredible, it's far more likely that your management will be about selecting presets and locking strangers out with a password. With ArenaNet in charge though, nothing is certain...