Good points.
Personally, I rather liked the V5 Coldfire cpus, available as salvaged parts, but they aren't well documented.

And we are using PPCs, so your point about NXP's first 64bit core makes sense.

Also, the CPU is only part of the equation.

And if we want to drop prices even lower (again w/o an mmu or GPU) I can grap CMOS 68HC000FN20s for about $4.00.

Really, for our purposes, only using something reasonably powerful makes sense.
So up to X64 (or Power9) seems only right.

I'm just spending my weekend playing around with old retro stuff that defies reasonable arguments based on performance or economics.

And worse yet, now I've completely derailed this thread.

So out of curiosity, when are these trials set to resume?
Pity that this case is being heard in Washington State, if it was in Delaware there might be an opportunity to find out more about it.