As it turns out, it’s undetectable on x86-64 (or at least not reliably) which does not come as too much of a surprise.
I don’t see any way out of a declaration.
A new PEP is indeed required, there’s some discussion in What to do about GPUs? (and the built distributions that support them) - #85 by bwoodsend & Selecting variant wheels according to a semi-static specification
The RISE riscv64 manylinux images take about 3 hours to build under qemu-user on such a machine. If this were an acceptable path forward, I would of course be happy to open an issue to discuss what the riscv64 image should look like and to contribute/review/test patches.
I propose to delay the discussion of the image being built in the manylinux repo pending the PEP.
In the mean time, I wouldn’t mind reviewing/integrating some patches in the manylinux sources if that helps get things moving forward (most likely would need to be based on the armv7 support which is currently a draft pull-request but probably not for too long).