Direct Drive vs. Idler Drive vs. Belt drive

No argument theophile. But no where in audio history except Edison was such a big step taken by one guy. Not only did he invent the suspended belt drive turntable but the woofer design used in at least 1/2 the subwoofers and speakers made, The AR 1. He started by cutting up an Electrovoice woofer and making a new spider and surround for it. It worked.
AR had 33% of the a very competitive speaker market. He was not the only show in town. 

looscannon

The AR XA was a ground breaking turntable. Not only was it less expensive than everything else. It was also better performing and not by a little. It's only over site was the lack of anti skate.

The AR turntable was indeed groundbreaking and its three-point suspension design has been widely imitated and refined. But the pickup arm was just awful. AR used somewhat better arms in later iterations of the design, but serious AR 'table owners chose their own.

By today's standard it is not so hot but back then not bad at all. An SME arm cost twice as much as the whole turntable! If you put anti skating on it along with a real horizontal bearing it would be quite competitive.
There are aspects of the XA tonearm's design that are very important. It is a neutral balance design. It's vertical bearing is at record level. It has a very stiff but light head shell (it just happens to look cheap) These aspects of design are critical for the best performance. The Kuzma 4 point arms are designed this way as are the SME and better Origin Live arms. The crazy expensive SAT tonearm's vertical bearing is way up in the air and it is a static balance arm! I don't know about you but I would never consider one even if I had that kind of money. If you don't believe in warp wow raise the back of your arm all the way up, put on a test record with a steady 1000 Hz tone and stick a nickle under the edge of the record. The tone will change very noticeably as the stylus passes the nickle. Now drop your arm so that the vertical bearing is at the level of the record. Very little tone change. IMHO the SAT arm is an extremely well made paper weight. 

Lewm,
you are right. 1 motor + passive flywheel on opposite side to nullify any side forces on the bearing. As I do with my original Micro Seiki flywheel. In case of the two motors you need to have an intelligent adjustment incorporated in the motor steering, as VPI or Sterling do.
Unfortunately VPI is not producing their SDS steering anymore, but they developed the ADS.

p.s. I am wondering why TechDas did not incorporate such a solution, the Apolyt uses an inbuilt passive flywheel

best
E.

Passive Flywheel = more mechanical noise. It is the same reason manufacturers interested in the highest fidelity shied away from changers and idler wheel designs.