I think ideally you want a guy who can play many MF positions. One of the issues with Pirlo, especially now given his age is he is only effective as a regista. If you buy a versatile guy (examples: Modric, Pjanic, Nasri [Surprisingly, yes - look it up], Oscar, Thiago Alcatara), those guys can play every central midfielder position and in Nasri's case, he can play on the wing.
I think that is the type of players Juve should buy especially given the formation experimentation that Conte likes to employ. There is no doubt he wants to use a 4-3-3, and he has spoken of a 3-3-4 before as well. To be able to experiment in that fashion, you need VERY versatile players.
Just to illustrate examples - this an illustration - and would never happen...
4-3-3
Cuadrado-Tevez-Di Maria
Vidal - Modric - Marchisio
Coentrao - Chiellini - Barzagli - Lichtsteiner
3-5-2
Tevez - Llorente
Di Maria - Vidal - Marchisio - Cuadrado
Modric
Chiellini - Bonucci - Barzagli
4-2-3-1
Tevez
Cuadrado - Modric - Di Maria
Vidal - Marchisio
Coentrao-Chiellini-Barzagli - Lichtsteiner
3-3-4
Cuadrado - Tevez - Llorente - Di Maria
Vidal - Modric- Marchisio
Chiellini-Bonucci - Barzagli
IMO you gotta buy players like those that I mentioned, where they can play more than one position well.