I did think it was telling we lined up in a 4-3-3 at the end of the season. Maybe Vanney feels the 3-5-2 has grown stale or too predictable.
I don't think we have the right personnel exactly to play it though. I'm very skeptical of playing Giovinco as a winger. He could drop to CAM, but then we only get one of Vazquez and him on the field. He could play as a false 9, but then where does Altidore (or a potential replacement striker) play?
If I'm guessing right now I think it might be something Vanney wants to incorporate for flexibility when we have injuries and absences, but not necessarily the go-to look with a full squad.