As pointed out already this comes from the twitter feed - there will be a full announcement tomorrow (Seattle time) on the ArenaNet blog
so watch out for that if you're interested in following this more closely! (Source
For those who might not already know, the weekend of the 27th is also Guild Wars' 7th birthday. This has always been celebrated with an in-game event, the fact that the first GW2 BWE shares the same date raises some interesting questions... perhaps ArenaNet have been planning something special? ...Or perhaps they haven't because they've been too busy with GW2 and they'll just re-run the same event from last year in the original Guild Wars
They also recently announced "A New Look for GuildWars.com" and in that announcement said it was due at the end of March. It hasn't appeared and they've gone quiet on the subject, perhaps another indicator something special is in the works!
Speculation is fun anyways