Interesting question.

It will probably depend (to some degree) on your application, and your target user.

A site like tribe.net will very likely have an overrepresentation of introverts-- so you could certainly study attributes of the introspective e-types, and factor elements of what they think is "important" in life into your original usability blueprint. For example "privacy issues" might be more important to introverts, than extraverts. If the "social context" has a theme (as opposed to a "general" approach), you might be able to dig even deeper.... an application that focuses on the "psychological aspects" might draw disproportionately many e-4s (studying self) and e-5s (studying the workings of the world).

Not sure if I'm making sense to you, here-- and I'm sure there are many other possibilities. Overall, though, I think incorporating the knowledge of the enneagram would be more relevant to "situation specific" applications, as opposed to "general" ones.