Doing that at a startup would be easy, since you control the whole stack and can tune it to the use case, and almost certainly don't have problems of scale. It'

Doing that at a startup would be easy, since you control the whole stack and can tune it to the use case, and almost certainly don't have problems of scale. It's 90% getting the technical stuff in place, assuming you have the budget. Doing it at a place like Google is a different matter. The job isn't tuning a stack. It's coordinating multiple teams that own different services, and trying to make general-purpose services and frameworks work especially well for a specific case, even in the face of competing demands and standardization forces. It would be 90% political, and the task-specific differentiation required may simply be insurmountable - the extra wrinkles for your use case might cost more in complexity and reliability than it's worth.