External stepper drivers and paired with the right stepper has such a huge speed range. A good example is a nema 34 motor and driver on my router table. I can run at Cutting speeds as slow as .125 inches per minute just as smoothly and accurately as cutting at 6 inches a minute. That is 48x the speed change, well with in the limits of my steppers and drivers. My gantry weighs 328 lbs, when not cutting I can run it at .065 inches a minute without stalling and max rapid speed of 150 inches a minute, again no stalling.
I really can not see a problem on the driver/stepper end of it running a telescope mount in tracking (which I believe is .04 deg/min) to slewing at 6 to 15 deg/s a minute.
If there is a problem I believe it would be needing to adjust the coding to allow such speeds and in the physical limitations of the scope and mirror mountings.
San Jose, CA