I agree about the cloud having the potential to be a good fit for CI builds, but I don't think it's there yet as there is a time overhead with turning on and off a cloud VM. Ideally, we would have serverless functions doing this, but most cloud providers limit the run time for those. Another problem is that a lot of build systems are single threaded, and the chances of finding a server CPU that runs outperforms a 5Ghz home CPU are very low.