Okay, I removed inkscape.tcz from OnBoot and rebooted. I then replaced ImageMagick.tcz, *.tcz.dep, and *tcz.md5.txt in tce/optional with the ones from the 3.x repository.
When I entered "tce-run inkscape" on the commandline, it gave me some silly error twice and then started.
I can now start Inkscape without any errors.
The rulers don't seem to display quite right (see attached image* ), but there is an option to not display them and this probably an "upstream bug"
*Oh never mind, my internet connection is being stupid again