For those who don't know, one of the biggest Twitch streamer is playing Gw2, he averages 30k viewers every day.
Anet already tweeted about him but I think it can pushed a little further.
My suggestion: An Anet GM that is very experienced with all the gameplay and content, reach out Summit1G, join him in voice and answer any questions he has about the game during his live stream, give him a code to activate the expansions on his account so he can play HoT and PoF advertising the expansions.
Give him a couple codes to give away (people love that), it could be Mini, skins or whatever you want.
That's just a suggestion, I'm not pushing anyone to do anything or demanding it. I don't know if Anet will do anything but I can only hope. It's a good oportunity to advertise the game for thousands of new people.