The linear tracking arm is without doubt a better setup than any pivoting arm, but the friction of the arm when it travels has to be reduced to near zero. Most linear tracking arms use an air bearing which is complex and delicate, and the air compressor is noisy.
There is, however, another approach which is used by my Sony PS X800 turntable. The arm is moved by a servo motor, just like the arm which carried the cutting head when the recording was made. The movement speed is biased to match nominal groove spacing, and then that speed is varied to match the actual groove spacing as measured by any angle of the arm. The arm is not fixed perpendicular to the track, but can pivot slightly: the servo moves the pivot point. The servo is well designed and does not exhibit any of the problems that some folk fear (hunting, oscillation, etc). Tracking error is maintained at less than 0.05 degree. Note that the servo approach is equivalent to a completely frictionless bearing. There is no sideforce on the stylus...not even the tiny force needed to move an arm with an air bearing.
There is, however, another approach which is used by my Sony PS X800 turntable. The arm is moved by a servo motor, just like the arm which carried the cutting head when the recording was made. The movement speed is biased to match nominal groove spacing, and then that speed is varied to match the actual groove spacing as measured by any angle of the arm. The arm is not fixed perpendicular to the track, but can pivot slightly: the servo moves the pivot point. The servo is well designed and does not exhibit any of the problems that some folk fear (hunting, oscillation, etc). Tracking error is maintained at less than 0.05 degree. Note that the servo approach is equivalent to a completely frictionless bearing. There is no sideforce on the stylus...not even the tiny force needed to move an arm with an air bearing.