I have owned several linear tracking arms.
Air bearings don't work. I am sure all of you have noticed that the more pressure you put in the arm, the better it sounds. The problem is that there is a violation of a fundamental turntable design rule, which is this: for proper LP playback, there can be no bearing slop between the surface of the platter and the cantilever of the cartridge.
Air bearings by definition have bearing slop, and this is why they sound better as you add more pressure.
The other problem, already mentioned, is that due to the excessive lateral tracking mass, it is the cantilever of the cartridge that defines the tracking error **not the arm**! This is because the cantilever has to flex to move all that mass.
The result is that a good quality arm like a Triplanar or Phantom has lower tracking error than any air-bearing arm!
In order for a straight-tracker to actually do its job right, it cannot have any slop in any of its bearings. Linear tracks do exist that have no slop, so it would not be that hard to devise an arm that also has no slop, using a servo not unlike what the old Rabcos used (updated of course). Arms like that don't exist right now so for the time being, radial tracking arms rule the State of the Art roost.