Ding ding ding. And technical reasons aside, what I find ironic about some Apple users here suggesting ducked-taped solutions over more elegant ones is the fact that Apple themselves are about not only using elegant design, but using the right design / interface for the right situation. (Which is why you didn't see OSX desktop on phones.) iPads and iPhones are for one type of use case, while CarPlay is for a different case entirely - driving - with added safety and convenience issues to keep in mind. Bigger, simpler and less distracting UI than that of typical iOS apps is most certainly a necessity to put everything at a fingertip on a dash, something you often control without taking your eyes off the road (touch screen or not).
My old trusty 2006 aftermarket is due for an upgrade. Originally I got it when iPods were popular and that's all it officially supported, but I found that my iPhone not only charged but played audio straight through the docking cable with nearly any program, so long as music from the iPod application played first upon start. However, it doesn't always support some of the more modern things like controlling music skipping through the dash itself, requiring using the phone, which I won't do on the road unless stopped. And especially with iOS7, I often get the dreaded "Error 01" message when the phone does something the head unit doesn't like. So time to update and I'm glad I waited...interested to see where CarPlay goes. If I can get GPS on it along with Podcast / simple Spotify control (as Apple already advertises it will have), that would be worth it to me, but I'm interested to see if more of the development area opens up in the future.