It would all depend on whether audio continues to "get better" at the same pace as the rest of the game, (graphics, AI, etc) or at a slower pace, or a faster one. I would assume that audio will get better, just because it can, but enough better that it continues to be a signicant load on the CPU? I don't know.
I believe the audio engine of Forza 4 was consuming an entire core on the 360. (Car games are notorious for the number of sounds they need to manipulate.) That's a full one-third of the 360's total CPU resources, in a game where the CPU was desperately needed for other things, like physics. If some PS4 car game attempted to do something similar, but at a higher quality, It doesn't seem impossible that it might burn an entire Jaguar core. It would certainly be an option, and options are a good thing.
Again, more CPU is always, always, better. Even if it's just a little better, developers will happily put it to use.