The Epcot Flower & Garden Festival goes through May 18th. While not quite as popular as the Food & Wine Festival in the Fall, it's still very popular and has a big impact the Epcot resorts' availability.
Only about 20% of the rooms at BWV fall into the Preferred Boardwalk View category, as opposed to the Preferred Pool/Garden category, which is about 60% of the resort. You never know when pixie dust will strike, but this is one of those hard-to-get categories. Don't be surprised if the waitlist doesn't pan out.
Waitlist notifications are hit-or-miss. Sometimes you'll get an email or hardcopy booking confirmation in the mail. Sometimes you won't. It's a good idea to check online from time to time if you haven't heard anything.