The thing with Pirlo in a "4-2-4" is that it's better for him offensively. There's more space in the middle of the park because our wingers are forcing the enemy to stretch themselves.
The problem will be defending but I hate when people say he can't work in a 2 man midfield because he sure as hell will work offensively IMO. We just need the RM and LM to run a bit extra and have the SS drop down a bit, sort of like a 4-2-3-1.
Dude, have you been paying attention over the last few years? Even with the straight 4-4-2 we don't stretch anybody. It's not just because Marchisio is used out left sometimes... the lack of East-West movement causes the system to be very static. If Conte doesn't fix that, so what if we have a lot of width. It's not like Pirlo is someone who drives through the center anyway, he's a regista.
So in regards to the offensive aspect of the game, the system doesn't exactly matter. If you don't have movement you'll fail either way. But at his age, it's the defensive facet of the game that we have to worry about if Vidal doesn't deliver defensively.
The 4-3-3 thing is a myth. He always played better for Italy in a 4-4-1-1 with Camo and a half winger like Perotta.
And Milan used to play 4-3-2-1 with WC AM's like Seedorf and Kaka.
It isn't a myth because you're using the younger Pirlo as the example and with Perrotta out left he at times took a more central role. I see what you're doing... you're basically advocating using Marchisio out left again. And that's not going to fly with me or anybody apart from Marchisio fans who want to force him into the starting XI in any way possible.