No way? So Vieira was just blow in smoke when he told everyone that his philosophy was going to be getting players in position to succeed as a team, and that could be 3 or 4 at the back? There are a lot of other areas he could have used as an example, by he chose one that is very odd for the league.
Combining everything I heard out of his mouth a couple of weeks ago, I think he definitely wants 4-3-3 long-term. But I think he's going to focus on mentality and purpose, then find his best 11 players and organize them in whatever suits his tactics. If Pirlo needs cover, parking a sweeper CB back there isn't the worst idea, as it frees your attacking talent, letting them have more freedom to leave the Maestro and head upfield. Basically, you end up with a formation that in attack, looks a lot like what Columbus does. We won't attack the same way, but that's what our attacking shape would look like in my mind if we went 3 or 5 (semantics) at the back.
I think this is flawed, because by adding a third CB we are actually pulling one attacking player off the pitch.
If you have three in the back and they're only playing one striker, we are massively overstaffed back there. When facing a 4-3-3, a three man backline is stretched wide and leaves gaping holes. A three man backline pretty much only works optimally against a 2-striker formation.
Four in the back is just so much more flexible. If they play one striker, your fullbacks can bomb forward easily. Against a 4-3-3, we still have the numbers to easily cover. Against a 2-striker formation, the fullbacks take turns bombing forward.