Interesting comment by Rob (beta tester).
If the dev set the flag originally in their product (Global Environment map reflection) then you'll see it ... what it would do prior to this new P3D feature is just reflect a generic static scene (think it was landscape mountains or something), now with Dynamic Reflections enabled it will reflect the surroundings as you move thru the world, whatever those surroundings maybe.
Dynamic Reflections can be enabled for ANY texture/surface, so yes a metal plane IF the developer enables Global Environment map reflection. Be aware that developers could still do their OWN custom dynamic reflections, but now it's just a lot easier.
Best way to see what does and does not have Global environment map reflections is to turn dynamic reflections on/off in P3D and see if you notice a difference in the aircraft/object. As has been pointed out, PMDG windows, Q400 windows will show dynamic reflections as they set the Global Environment map reflection even thought they knew it would just reflect a static image when they original created the aircraft ... but it looked like a reflection back then even if only static, so they used the flag. Now it will be a real dynamic reflection of the world one is flying in.
So expect more 3PDs to start using the Global Environment map reflection in future products (or some may even update existing products) now that they know it works dynamically.
Dynamic reflections is a "huge deal" IMHO and when 3PDs start using it more our FPS will be impacted (if we enabled dynamic reflections), hence my warnings. So save up for that next gen GPU and CPU if you want to claim you can max everything out and get 1000 FPS
Yes, it's progress and hardware will always need to catch up ... "as real as it gets" will always mean "open your wallet".
Cheers, Rob.