I think the easiest solution at the current time is to run the Coverity
scans on one or two parallel machines that harvest successful build
results from the actual Extras buildsystem, and which non-Red Hat people
don't have shell access to. Furthermore, this ensures that released
Extras packages are fully externally reproducible, since the Coverity
scanner sits between the build scripts and GCC. The web-based reports
portal would be still be accessible to package maintainers of course.
Like Warren says, then there's no slowdown for the build system, we stay
clear of any difficult contractual or legal issues related to access to
Coverity binaries, and the packages are completely externally
reproducible.