It seems to me that these TT's provide the best tracing of a groove (not tracking as that's another issue) possible and I'm somewhat confused as to why they aren't more popular. I am no tech-guru (as you all well know), but on the surface this method seems to be a no-brainer.
Why aren't more companies producing such tables?
i owned the Rockport Sirius III for 8 years; it's generally considered the ultimate implimentation of a linear tracking turntable.
over time i had a number of tt's and arms sitting next to the Rockport to compare; and eventually it became clear that the linear tracking arm was a limitation when faced with the very very best pivoted arm. up to that point, the Rockport and it's linear tracker repelled all comers in an overall sense.
and the Rockport was a very expensive tt and arm to produce, and every part of it was engineered and built to the nth degree.
the question could be posed; if enough resorces were committed could a linear tracking arm surpass the best pivoted arm? my SWAG would be no; that the physics involved ultimately give an arm completely free to wiggle an advantage in ultimate resolution......and any linear tracker has limitations in getting leverage for ultimate bass performance to some degree by whatever arm-shaft interface is used.
all that said, linear trackers do bring certain wonderful characterisitics to the presentation in terms of scale, image size and stability, which only the very best pivoted arms can achieve.
the bottom line is that there are lots of people trying to improve pivoted arms so things have moved forward, whereas almost no one is throwing money and time at making better linear trackers.
now; speaking about vintage linear trackers we have a multitude of issues to throw out. chief among them is that any mechanical linear tracker will crab accross the record however you slice it. it does take quite a bit of refinement just to deal with smooth tracking along the arm shaft. whether it's an air bearing or not. then you have different approaches to air bearings and their trade-offs.
lots of variables.
personally i would love for more efforts to happen regarding linear trackers. who knows what might be possible?