Currently the proxy related contracts exist both in
openzeppelin-contracts-upgradeable repo, this will cause confusion to users which to use.
And I think the one in
openzeppelin-contracts-upgradeable repo is the latest version, for example the
openzeppelin-contracts doesn't inherit
Initializable but the one in
openzeppelin-contracts-upgradeable repo does.
IMHO I don't think there're real scenarios where proxy is NOT used for upgrading purpose, so maybe removing proxy related contracts from
openzeppelin-contracts repo is the way to go.