In round numbers, coreboot is at about 5k commits/year (last time I looked; maybe it's higher or lower now). Assuming each CL takes around ten builds, that's 50,000 builds, times 350 boards, which translates to "a lot." It keeps Martin's house warm, I suspect. That's not counting the continuous builds that go on for Chromebooks at Google, Intel, and many other places. These builds all include Quark.
This specific information on what kind of tasks retaining quark can burden is productive.
If people preferred to retain quark, it could be important to address things impacted by that choice.
Other approaches to this burden could include reducing the frequency of inclusion of boards within CI if their subtrees were not touched by intermediate commits.