You guys really think this functionality is going to be available soon in aftermarket units? Doubt it, think about it, it is available for 6 car manufacturers now and another 12 down the road (probably next year). Dealerships will charge you for this high end system on their new cars. People will not pay top dollars for it if it is available for less on an aftermarket unit. I'm guessing it will only be available from the car manufacturers for a couple of years before its available in an aftermarket unit. I'm hoping that I am wrong.
Look to history of the aftermarket to get an answer here. Just like cars it takes years for aftermarket radios to be properly developed. If apple has been working with the aftermarket ahead of the launch of carplay it won't be very long of a wait for an aftermarket solution to arise. However if the first time pioneer or alpine heard the words carplay was yesterday then expect to wait a while.
Now there is hope here. Siri eyes free was announced in mid 2012 with the announcement of iOS 6 and aftermarket radios featuring Siri eyes free came out just one year later. This leads me to believe that apple isn't leaving the aftermarket high and dry. With that in mind I'm sure that apple is working with the aftermarket to get this solution to users.
Apple knows car buyers don't change cars every year like phones. Apple knows that to get good developer support for their new interface it needs to be in as many cars as possible. As such I don't doubt that they are working with pioneer and alpine and everyone else to get this through.
Finally remember that these same companies produce radios for the major auto manufacturers. Pioneer for example seems to run every radio in every current Toyota. So apple is working with the aftermarket by proxy when they work with the OEMs. I'm not worried.