I've setup on-prem environments that would automatically and transparently spill workload to the cloud when we ran out of on-prem capacity. The prerequisite is that your operations people need to have strong automation skills, there can't be any human button-pushers in the loop, but it really isn't that much work nor does it require unusual technical skill if you have a competent operations environment. Once everything is wired up, it mostly just works. Even the devs often don't know whether their workloads are running on-prem or in the cloud.

An under-rated aspect of this is that it provides detailed data for planning the expansion of the on-prem environment, including changes in how the hardware is being used.

My experience is that this is a good model. On-prem is about 1/3 the cost of the cloud, fully burdened, in my experience but being able to transparently spill to the cloud mitigates the capacity and supply chain risks that come with on-prem.

It is effectively a cheap insurance policy.