I've compiled erlang R14B01 with the following ebuild: https://github.com/billiob/gentoo-overlay/blob/master/dev-lang/erlang/erlang-14.2.1.ebuild It's erlang-14.2.ebuild with just the version changed (MY_PV="R$(get_major_version)B0${ERL_VER[2]}", adding '0'). Tested only on amd64.
Needed only one more tweak (a patch would not apply but is not needed anymore anyway). Bumped, thanks for the report.