I found this: https://en.opensuse.org/openSUSE:Build_Service_Concept_CrossDevelopment
I suppose the OBS cross-compile option isn't quite ready yet then. It would be helpful if cross-building were better supported though. Aarch64 targets do not require any kind of emulation for armv7 chroots. I think building with chroots could be a solution if better support was there. Maybe someday though.
