I've built a couple of test-bench "bed of nails" devices for a customer using RPi model 2B's from a couple of years ago [with the older BCM CPU on them]. Also have a model 1B and another model 2B that I'm playing around with at the moment [writing necessary kernel drivers for FreeBSD].
I saw that after I bought my Pi 2's (and the ones for the customer devices) the CPU on the RPi 2B v1.2 was updated to a 64-bit device, though from what I have read it also runs the older 32-bit code, which is good, because I do _NOT_ want to be forced into a version of Raspbian that uses systemd... [and so I should be able to continue using FreeBSD and the older Raspbian on it]. Haven't tried Devuan's RPi code yet (Raspuan?).
I'll still have to try the 32-bit OS's on the RPi 3 though. anybody done that? As far as I can tell it should work.