A prototype is a great way to get the conversation started. Most people don't even know why Vault should be considered, let alone why it's better than K8s secrets (which in their world works fine).
At its core, I'm having some difficulty wrapping my brain around the idea that any organization that's large and complex enough to demand to run their own compute platform (e.g. K8S) isn't also large and complex enough to demand a secure configuration system by default.