What's the deal with idler turntables and do they have a place in modern HiFi?

The "problem" with this hobby is that there are frequent instances where we have phenomenon A associated with physical fact B, and the natural human response to such coincidences is to ascribe A to B. But we almost never have good scientific experiments to prove or debunk such associations. Thus we are all floating in a sea of subjective judgements, and there is an industry based on tweaks that thrives upon our ignorance.

Very well said, Lew, IMO. I would add that in audio there are countless variables that can be cited for which it is not readily possible to define a quantitative threshold separating what may potentially be audible in some systems from what is unquestionably insignificant. In the absence of that kind of quantitative perspective there is essentially no limit to what a perceived or claimed sonic effect can be attributed to.

Best regards,
-- Al

Spot on - Lew & Al. 

One false link I alluded to above (my first rim drive experiment) relates to incorrectly ascribing massive torque as the reason for rim drive's attributes.  Actually, it's the architecture itself (rim drive) that is responsible for this. 

This isn't an argument for or against high torque, but rather (as you both stated) to not jump the gun in terms ascribing causality.  This of course goes further down the rabbit hole - that we may well have the equipment, but not know what we really want to measure.

Indeed, a Timeline is no better or worse than a KAB, and at the speed level of granularity responsible for intermodulation distortion, the Feickert is also useless.  At this point, all I can use these tools for is to observe a (likely) loose correlation with what I and my listening panels are hearing.

Cheers,
Thom @ Galibier Design

There is also a price to pay when the platter is massive. Light weight platters have been preferred by any "well-designed" TT designers for the same reason.

I am yet to hear any belt drive turntable sound like a direct or Idler drive in resolving the pitch and rhythm of music. For some it is not very important.

Pani, I think your generalization about light weight vs heavy weight platters is very much open to debate.  One could just debate your point that light weight platters are a given in a "well designed" product, but is it really worth the trouble?  Seems to me that there are many great turntables, especially of the belt-drive variety, that take advantage of massive platters.  But yes, I agree, there's a price to pay, just as there is a price to pay to optimize any design choice.  I also share your predilection for idler- and direct-drive vs belt-drive, but because I have held on to that bias for 4-5 years now, I feel I need to keep an open mind; I've lost touch with the belt-drive sound and no longer feel qualified to reject it out of hand.