The linked bug report should be addressed, but that does not necessitate keeping AUR/libopenblas.

As there is no lib32-(lib)openblas package and nothing in AUR seem to need a multilib version of openblas.

Also, AUR submission guidelines also mandate no copying of repo packages to address packaging bugs/requests, but to have them resolved via bug report.

As for x86_64 builds on AUR requiring openblas, they should find the CMake files of repo openblas package just fine.