Wolfram, is there a better way to get something stable for user space to
interact with? Is there maybe a way to do this with aliases or something?
Setting up an ad-hoc scheme for forcing the adapter IDs feels a bit outdated.

Yeah, it feels rightfully outdated IMO. Bringing such policy into the
kernel is frowned upon. I think the proper way is a udev rule to act on
the newly created I2C adapter. This even could provide a really stable
symlink for userspace to consume. The above scheme is only stable per
"block" but inside the block, there is still randomness. Or?