At this point the E3 LL on the 14th is probably the best bet for a main theme song trailer. There will definitely be a theme song because we've already heard parts of it in the cinematic trailer. They usually release it a month in advance, so this one is off schedule. I'm guessing the crunch for ShB is much worse compared to the previous expansions, or maybe there's some other reason they want to keep the song under wraps? Who knows. I'm sure there will be one, but it does seem delayed this time around.