I would bet they still burst-out to AWS. For me the logic is more like: get cheapers machines (be it in-house or with cheaper alternatives), that run kubernete

I would bet they still burst-out to AWS. For me the logic is more like: get cheapers machines (be it in-house or with cheaper alternatives), that run kubernetes for example, and monitor them with Prometheus. If you run out of capacity, defined by whatever metric you fancy from Prometheus, start EC2 machines for the burst. Every month, re-evaluate your base needs.