Oh hey, so that’s how you found my thread; you’ve been thinking about related things! 
I believe it’s a great idea, and something like this would in fact be necessary to what I am talking about in that thread: a standardized way of storing profile data and also presentation (e.g. banner image, color scheme, …) that can be used by apps to display whatever they want.
For profile data, why not use something existing, such as (maybe subsets of) vCard or jCard or FOAF?
Applications could provide their own methods for rendering, e.g. in the form of an HTML template (but the details are really the app’s own business; they for example could opt to not use any of the style information provided by a social profile.)
To be honest, the idea of having custom templates for profiles kind of clashes with a proposal I had; it’s about themes for accounts.
My idea of theming would affect the way apps appear for the user whom the profile belongs to. This would act as a safeguard against apps impersonifying SAFE apps: the themes are only visible to the user themselves, so only after a successful login could an app display them. If something doesn’t show up with the proper theme, it’s not a legit app.
Also, different identities of the same person (i.e. sub-accounts) could have different themes, which would help users avoid embarrassing mistakes.