to try to look at the physical implications of this...
the flipper rests I've seen would raise the arrow height at the "shelf" by about 1/8" to 3/16"... I know that some folks are quite concerned about tiller, particularly of the lower limb. Some are concerned about special tillering of the lower limb to accomodate 3 under shooting vs. split.
So, my question would be how much effect would putting a somewhat raised arrow support have on the bow, in terms of changing that tiller?
As far as the "is it trad" issue goes, these flipper rests were almost standard way back when, on recurves. For myself, I shoot for fun and don't score, so it wouldn't be an issue, though I guess it would look funny on my Hills :^)
Dick in Seattle