I do not foresee any problems with the new phone and ios8, as long as the app developers keep abreast of their apps and update them accordingly.
And therein lies the rub.
Pioneer's track record with adding support for new phones to the AppRadio has been piss-poor. Example: the Samsung Galaxy Note 3 was released last September and has sold upwards of 15 million units. To put that into perspective, that's almost half as many sales as all models of iPhone combined, and yet this phone, the Galaxy S5, and other popular phones running the latest versions of Android are still not on the "supported" list and do not work correctly with AppRadio mode on the NEX.
Now maybe they have all their software developers focused on CarPlay and don't have the resources for anything else. Maybe Apple will hold them to higher standards and the inital release of CarPlay functionality on the NEX will be smooth, seemless, and bug-free. Any maybe monkeys will fly outta my butt. 
I do hope I am wrong. If CarPlay turns out to be a clear win on the NEX, my next phone upgrade will be an iPhone 6. But after seeing what a klunky mess AppRadio Mode is, I'm not very hopeful that Pioneer can pull it off.