Here's some thoughts from another source that I have queried on this topic:
"I think the only way to go is with a matched fit with 3 point engagement on the outside diameter of the platter so you don't give up concentricity and minimize resonance transfer. If you locate the ring on the O.D. of the vinyl record, you're depending on the record being pressed dead on concentric and this rarely happens. The ring then rotates about the same eccentric axis as the record and destroys balance."
An interesting thought for sure about a non-concentric record's problems being emphasized by the ring. I like the thought of there being some kind of centering mechanism for the ring, to ensure concentricity, but implementing something that is also user friendly (given that a ring is generally NOT user friendly to begin with) could certainly pose a design challenge.
As for the brass platter plate, my mind is still uncertain on this one. I like the design of my black VPI platter, where the record and the platter are similar and rather effectively coupled via the VPI clamp. I may wait to see how that one fares on your rig Dave :-)
Bob