I'm often asked: Should all application workloads exist in the public cloud? The right answer is one that most people don't want to hear: It depends.
It depends on what industry you're in. It depends on performance expectations. It depends on security requirements. The list goes on. Some enterprises will reach the point where 80 to 90 percent of their workloads exist in the cloud: some will only get to 50 percent.
There is a point at which it does not make sense to migrate any more applications to the cloud. This is due largely to the fact that there is no significant economic benefit in doing so. It doesn't make sense to migrate what doesn't pay for itself.
This is why I insist on making a business case that outlines the business benefits of moving to the public cloud for each and every workload. Most business cases are obvious, some will need deeper study, and some will fail to show any value. When it no longer makes sense to migrate any more applications to the cloud, you've reached your natural saturation point.
Despite the fact that it will take many years to reach that saturation point, you can actually calculate today what that point will likely be. It's just a matter of doing some deep analysis on your existing workloads to figure out which ones can go to the cloud and which ones can't.
On the other hand, who can predict the future, especially the future of technology? In five years, the cloud may have evolved enough that there will be a business case for those applications that initially did not make sense for migration. Still, it's a safe bet that all applications won't move to the cloud, even as cloud technology gets more cost-effective and better at addressing workload needs, such as compliance, security, and performance.
The chances are good that you'll find the saturation point sometime in the next five to ten years. That is not a bad thing. It is an even better thing if you understand where that saturation point is by thinking pragmatically about the use of the public cloud and justifying everything you move. By doing so, you'll save money, time, and disappointment.