Currently, to use Android Auto, you either need a vehicle that has it built-in (like the Audi Q7, A4, Chevy Malibu, Impala, Sonic, Volkswagen Golf-R and many others), or you need to buy a third-party head unit and install it into your car. Neither option is necessarily "cheap" and it is why we haven't really seen Android Auto take off, despite it being available for over a year now. At Google I/O back in May, Google announced that they would be bringing the Android Auto experience to the car in the form of an app that can be run on your smartphone or even a tablet. Making us ask the question, is an Android Auto compatible vehicle really necessary?
Well, if you have the option, having Android Auto compatibility in your next car is going to be a big thing. It'll offer things that the app simply can't offer. Like steering wheel controls - which allow you to send messages, change the music and give other voice commands without touching the display, and most importantly keeping your eyes on the road. But that doesn't make it a deal breaker, for many people. Especially since you do need to plug in your Android smartphone each time you get into the car. Using Android Auto can be a bit cumbersome, and it's something that not everyone is going to use on every trip.
With their being an official app - coming soon, of course - it means that you can buy a Toyota vehicle and not worry about them not wanting to have Android Auto in their cars. Because you have the Android Auto app on your smartphone. It's actually a pretty great way for Google to get around auto-makers that don't want to put Android Auto in their cars, while still reaching those drivers. So, not having an Android Auto compatible vehicle is not a big deal, or at least it won't be when the app is finally available - which will likely be around the time that the new Nexus devices come out. But it is still a nice feature to have, just don't pay extra for it.