FHS is not very specific on the exact use of /opt and /usr/local. What do people think of the following convention:
Use /opt for RPM-managed software that is not part of the Fedora distro, and use /usr/local for Makefile-installed and other non-RPM software. The /opt convention would only be for applications, and not for extensions or modified forms of standard packages where using /opt would be more difficult.