According to a Reddit author who posted what appears to be an HTC Release Note, the company is working on a device called Cello that is expected to integrate with cars more than Android Auto does. The features on the device include "Night Vision, Sonar, Mini HMI (Human Machine Interface), DVD, Tire Pressure Monitoring System, Lane Departure Warning System, Navigation and GPS."
Interestingly, the device will come up with a special version of HTC's Sense UI made especially for cars. This is called Sense Automotive and on the current version of Cello, it runs over Android 4.4. Of course, this could be updated to Android 5.0 or higher by the time HTC unveils Cello.
Some of the features listed in the Release Notes are capabilities not available with Android Auto at the given time. HTC has reportedly been testing Cello since the fourth quarter of last year when it was named Autobot. There is no word on when we might see HTC introduce Cello.