The biggest sell for Black Sun's Zenith in U/B control is that it shuffles your deck. When I'm pulling GARBAGE from Jace 2.0's brainstorm ability I can play a Black Sun's for 0 (along with the black cost) and shuffle it into the library then get a new pool off of brainstorm. Boros sucks when they get huge guys but that's when Jace 2.0's boomerang comes in handy. Plus I HAVE to wait until I can generate the 5 for Consume the Meek. 2-3 Black Sun's Zenith should be the staple for U/B now.
I run 2 Black Sun's Zenith in my mainboard at this point ontop of 3 Blades, 2 GftT and 2 Disfigures. Preordain and Jace 2.0 have successfully found me BSZ everytime I've needed it in games when I need them, and my mainboard isn't set up to exclusively handle aggro match ups, but to maximize on a variety of different decks before sideboarding.
After sideboard I'm running
Basically if they don't overwhelm me in game one, their chances of success game 2 and 3 is basically non-existant.