I’m very excited about this idea, especially from the MSME angle, and have been running few tests. So far, on a clean raspbian install, MariaDB should be installed without any hitches (provided that the original repos are unchanged).
I would have to assume that the problem with installation of MariaDB is specifically isolated for the case of ERPNext repos being used, that still might be pointing to x86 or x64 versions. I would assume one has to pre-install MariaDB and override the system installation, or modify the repo for the appropriate MariaDB version in the ERPNext package files.
Can anyone of you confirm this assumption on your individual Raspberry Pi installations?