Linear Tracker ...I was wondering

Terry9, I won't even look at an air bearing arm because of the problem of too much horizontal mass. The horizontal axis has to be driven and the arm has to have a passive horizontal bearing. Then you deal with tonearm effective mass like any other tone arm. Yamaha had the right idea but I think for the best motor isolation and reliability a belt drive would be best. It is however a tricky proposition. I believe a rack and pinion design would do it, the pinion being driven by the belt. Motion is so slow noise should not be a problem. The motor then has t have some type of servo control that predicts where the tonearm has to go. I envision a laser reading the groove just in front of the stylus. A groove is like the grand canyon next to CD pits. Should be easy to do. Unfortunately, small companies lack the technical horsepower to design this. It would be up to one of the big guys like Sony, Yamaha or JVC and they are not interested in such a small market. 
I encourage every straight line tracker owner to closely observe their cantilever tracking the record. If you see the cantilever drift side to side even just a little you have a problem. 

I also forgot to mention that the general feeling in the press is that the 4 Point is better sounding than the Air Line. 

I wouldn't be too concerned with the horizontal mass. Theoretically - consider the mechanical advantage of an inclined plane - the record groove. That means 100 microns of lateral motion in each revolution, during which the stylus moves about 70 cm, for a mechanical advantage of 0.70/0.00010 = 7000 or so.

Experimentally, anything like what you suggest should manifest on one side of the stylus, and quickly too. After nearly 1000 hours, my Koetsu shows very little wear, and what little wear there is, is almost perfectly symmetrical. (From a photomicrograph using a scanning electron microscope.)

Kuzma Air Line uses a high pressure air hose attached to a New Way amorphous carbon air bushing (mass about 30 g if I have the model right). That air hose generates a very large force, relative to the stylus in the groove - it supposedly provides the necessary damping. No wonder the 4Point sounds better.

Horizontal mass? Is that related to the horizontal mambo?

terry9"Theoretically - consider the mechanical advantage of an inclined plane - the record groove."

If you're records are an inclined plane then you need to level you're turntable because you're VTF and AS forces will be all over the place and you will suffer other playback problems if you're out of level with your turntable.