Meh, GW2 supports RP about as much as any other MMO does. It won't be a Mekka for roleplayers, but people who like the lore will certainly have things to do with other interested people. I'll roleplay a fair deal with select people I enjoy the company of.
Features that promote RP are hard to name, as they're pretty baseline from most MMOs (like chat bubbles and spacious, NPC-empty environments), but two things I can mention are the town clothes (already mentioned earlier by Rapti) as well as the area of town which evolves with your personal story. Also, a third is how easy it is for other players regardless of race, profession, or character creation choices to join your personal storyline and watch your events unfold.
I love how the world feels so alive. My first time in Divinity's Reach was overwhelming... NPCs talking together, moving to different places, talking to different NPCs,... Small children playing hide and seek, it's fantastic.
I'm talking not only about the cities, events change the world for a time... a nice push to be creative even out of towns to RP.
this video is full of those moments that make the world feel alive:
I think GW2 excels moreso than any MMO with RP interaction between player an environment, but I think Anet could add some things in order to promote RP interaction between player and player better. Can you even sit in chairs in GW2?
Anet could even steal a few things from LotRO, such as instruments. They also should add player or guild housing at some point. And it'd be awesome for them to create an event board where people could essentially make flyers for special events there are holding on the server.
As a role-player myself, I am glad to see that Guild Wars 2 is shaping up to accommodate my kind. We don't really need all that much to be appeased, assuming the game world is consistent, interesting and we get given the odd feature here and there that eases us into conversing and emoting with others of our kind. My biggest concern, however, is how the sinister aspects of our community will be dealt with.
As much as I hate to bring it up here, WoW is an excellent example of what I am about to highlight. For those of you who have heard of what Goldshire is like on role-playing realms...I am sorry to say that much of it is true. I really, really hope that GW2 has a strong and unwavering stance and that any weird fetish based role-play done in public results in a ban. That is the only way to discourage an entire sub-zone from being infested with people using role-play as a mask to hide crude and sexual wish fulfillment activities.
Though it is one of those issues that is often left unspoken. I don't think I've actually seen it officially addressed in any MMORPG beyond the odd angry parent making a thread about what their children have been indirectly or directly exposed to.
I think the new guild system will be a huge support for RP. Stay in your real-life-friend guild while joining a RP-guild and choose yourself when to represent/play for each. No more need for you to choose between your non-RP-loving friends and your RP-friends.