I've been inspired to think about this ever since I went to a talk last year given by Mark Doehmann, the designer behind the Continuum Caliburn turntable. What constitutes the plinth depends on whether you couple or decouple: for instance using a balsa baseboard sitting directly on my heavy support table couples the masses together, effectively creating a more massive plinth. As an experiment I added some HRS decoupling pucks under the baseboard, isolating the turntable from the support table and decreasing the mass, the sound was noticeably worse, less bass, less precise imaging.
From this clumsy experiment, I'd suspect that a PT can benefit from increasing the mass of the plinth, adding it inside the box is one way to do it, coupling the existing plinth to a heavy support stand or platform is another. Of course there are issues like footfall and vibration isolation to consider, but probably wall mounting something like a slate shelf would be the best type of platform for the PT as long as it is coupled to it, not isolated by rubber feet.
The sub chassis and platter are low mass and so won't store much energy, the idea should be to keep the energy out of the sub-chassis
Funked Pink Triangle, Kuzma Stogi Reference, Sound Smith Strain Gauge & SG-200 phono
CEC TL-51x, Apple MacMini, Amarra/Fidelia, Weiss Minerva DAC
Tandberg 3011, Octave HP500se -> active ADAM Tensor Deltas. Argento Serenity cabling