Hello,
Currently running Jessie with sysvinit/systemd-shim/cgmanager; thinking
about installing openrc.

I've been poking at eudev/reading the documentation/...; it's supposed to
offer ABI compatability with systemd libudev until that becomes too
difficult, but I don't have an ABI dump from the latter.
Does anyone else have that?

To get it, you'll need to partly build the systemd source (something like:
su -c "apt-get build-dep systemd"
apt-get source systemd; cd systemd*; debian/rules build
if I remember right)
Yes, that drags in a near-world of packages; you may want to snapshot a
package list beforehand.
Then run abi-dumper on the libudev.so binary, and save the "ABI.dump"
file somewhere.

Thanks,
Isaac Dunham