I can report back that I managed to finish the upgrade. I will report what I did but not sure exactly what solved it:
- I changed ssu release to 3.4 as it remained stuck in 3.3 despite some packages updated to 3.4
- as suggested here,
cp /usr/lib/zypp/plugins/urlresolver/ssu /usr/libexec/zypp/plugins/urlresolver/may have opened the possibility to rerun version–dup - I also did ‘pkcon download . ssu’ to manually update ssu package (following suggestion from @mal)
- I removed (not sure it helped) using pkcon: aliendalvik-control (even though I had updated to the version coderus said was compatible with 3.4) and storeman (the dev said it was not working until a fix)
- you have to wait for some time before version–dup completes. The first try ended up with an error message but an automatic retry worked.
- I could reboot. To make it safe, I rerun version–dup and indeed it found further packages to update
- another reboot and version–dup finally says no available updates
voilà I can enjoy 3.4 now 