Looking over what the Honda people have said in their tweets prior to tomorrow's full announcement, it looks like iOS in the Car will be a Wifi based Mirroring system nearly identical in principle to AppRadio, but most likely with a far better implementation since it will be an Apple designed system with deep under the hood APIs that Pioneer could never provide.
If this turns out to be awesome, I'm hoping an aftermarket radio comes out soon with the functionality. I have no plans to buy a new radio just to get the Apple upgrade.