The plan is to keep 352 till the very end of the cycle of our great CBs - 2018 World Cup.
A serious transition to a 4 men defense will only take place to the 41212 scheme, replacing a CB for a midfielder, instead of a forward - more gradual.
Only after 41212 is solidified, they will think about a serious change to 433 or 4132. That will take at least another season and a half.
And to move towards the 4 midfielders plan, we need the signing of a great/high profile one who will fit in and can perform in a way he can't be let out of the team, because Marchisio, Khedira and Pjanic are pretty much untouchable.
That guy will have to be Witsel or Bentancour, as it seems.
So, if a new great mid gets signed and starts performing, and everything goes according the plan, we should be using 41212 more often since january or september 2017, only to make it perennial during the 2018-19 season.