Will the P4 gain from it? Yes.
However, the current XPs are still quite fast, and high end XPs will still outperform several of the P4s even with some of the SECC2 enabled. How far reaching it will be, I'm not sure, because not every app can gain from it.
However, the XPs do have points to gain as SECC apps are streamlined as well. They have outperformed in apps that have been SECC enabled for the P4, and not for the XP, so it looks like we'll have to take implementation one code set at a time.
Chesnuts roasting on an open CPU
Bill Gates nipping at your wallet