This is a very interesting idea. I get the explanation provided on Medium.
One question. What problem will it solve? Is it to put an emphasis on the importance of stakeholders? Can it be done without calling it an accountability?
In my opinion, there might be some issues.
It’s difficult to expect that all stakeholders will inspect the Increment every Sprint. For example, some internal stakeholders have a low interest, and a high power. You only need to keep them informed and satisfied. We shouldn’t make them accountable, they would simply ignore it. And that’s OK.
Another issue is that it’s quite common that most stakeholders are not present during the Sprint Review and in many products most customers, which are also stakeholders, “inspect” the Increment after a release. Let’s take a YouTube as an example. Am I, as a stakeholder, accountable for anything?
Defining “Key Stakeholders” as an accountability may be some solution, but it will probably make this setup even more complex.
I feel that it is a PO’s accountability to identify and engage selected stakeholders, when needed.