Jack Douglas said:
Well they're asking for 1DX2, 6D2 etc. as trade - destroy?! Or are we to assume that no one having better gear is foolish enough?
Jack
Well some $6000+ Leica's too

I think they're on the list, just to be on the list, frankly, because nobody is going to trade in their 1DX2 for a $500 discount (if they're going to get an a9 and own a 1DX2, the $500 will be neither here nor there).
What I meant is that I doubt the traded-in 1DX2 will go back "onto the market". Sony could use them for internal R&D, but they wouldn't want the possibility that they could end up being resold, and re-enter the public market, because after all, the purpose of the rebate is to get rid of (one) high-end camera in favor of a Sony one. If I were a Sony employee, and happy with my Sony A9, but I got a cheap 1DX2, I might be sorely tempted to turn that into a Christmas bonus.
On the cameras like A7RII, they'll take any working camera, and I assume Sony doesn't want any of those to go back into the used camera market either, so destruction would seem like a reasonable thing to do, if they don't have a use for it.