You can just buy a Pentax DSLR which has a internally-moving sensor, and then buy the Pentax GPS unit that acts as an astro-tracker. Then the sensor moves with the stars according to GPS coordinates.

Also, if you're looking just for better image quality, a DSLR isn't anything special. It's just a camera with a mirror. You can get any APS-C or larger-frame sensor nowadays that aren't DSLRs.