Do there exist straightforward ways of (re)compiling raspbian (any release) for armv6-related ISAs, like armv7/neon? Maybe binary blobs could be reused, even under aarch64? Can you give some pointers?
Debian "armhf" and "arm64" automatically started working when the new Raspberry Pi models were released (2015 and 2016), except for video acceleration and camera support.
Raspbian is itself just a recompiled Debian targetting ARMv6 + VFPv2 instead of ARMv7. In 2012, no Raspberry Pi had an ARMv7 processor.
Debian "armel" has always worked on any Raspberry Pi and probably still does. Obviously the performance will be horrible.