Going to have to disagree with the raytracing part and have no opinions either way on the second paragraph other than DCS is a different simulator... how well does the DCS P51 handle in P3d? Does it handle worse or better than A2A's or in fact what are it's frame-rates like ? Oh wait...

Apples and oranges - 'tis a little tough to compare 2 disparate things.
Raytracing is early on. Look at UE4 for example. It has only been mainstream in the engine for around 2-3 months ( v4.22 ? ) the majority of people out there arent going to be able to run it on anything less than a 10 series ( and a high 10 series at that ) with acceptable frame rates. I dont know how the training organisations use P3d or not but I would have thought their budgets might not exactly allow for computer upgrades every year or so. I only know of the places near me in Australia and last I popped in there they were installing a "new to them " gtx 960". With LM's focus being training and not consumer... I'd have thought they would try to keep it at the lowest common denominator spec. So whilst I think your ideas on PBR requirement will be on point, I dont think they will jump 2 generation shifts. Especially since raytracing is such a young technology with relatively high requirements.