Create a buildset that randomly selects random images/machines/packages, builds them and then triggers itself.
Recipe-specific sysroots have probably solved most of the issues that would have been brought to the surface by this, since it should not be possible for missing dependencies to lead to non-deterministic behaviour anymore. I also have to say I am very skeptical of randomness in running builds for CI or testing purposes - there's a chance that you will miss running a portion of the tests regularly enough. If it were needed due to the time taken to run the full set, it suggests that we aren't providing enough resources to run the tests and/or we need to optimise what we are testing (in a targeted manner).