HST Robotic Vehicle Mission concept
details available for download here
The main goal is to set the HST for controlled reentry. The secondary task is to replace the batteries and fix the gyroscopes!
It will probably be done with telerobotics - a duplicate of the robot on the ground operated by an experienced HST-servicing astronaut.
Apparently there are a lot of motivated people pushing for this. Certainly will break new ground in telerobotics to say the least ..