While we're waiting for vdev (that does look like the way to go) I
revisited eudev, which I never managed to get working in a usable way.

Did much better this time after some not too major hacking of the source
posted on devuan git, mostly "rules" and "patches". I now got it working
seemingly (too early to be sure) quite well. My usb wlan device works,
other removables pop up normally and zero (udev) errors in dmesg output!

This did involve dpkg -P --force-all on existing udev components first.
Got a totally trashed system numerous times, which had to be recovered
in a chroot, before getting it going with yet another rebuild..

More later, after a little testing.

D