Yes please.

Creating an ID protocol that interfaces with a decentralised storage service would be incredible, or a separate service as OP describes (but using separate decentralised storage as a storage backend). I suspect it would need some flexibility as to the data objects, as different information categories are useful as a set depending on usage context (work ID vs social ID, different countries, vehicle licences of various types)

A user determined access structure to information would be achievable and highly desirable. For instance, why do Bitpay need to collect my name and address for their invoices? They don't have a legitimate use for the information themselves. Instead, a pointer hash to the storage location of the specific details could instead be attached to the invoice that the merchant can follow to access the information if/when needed, then accessed with a unique key that is issued to them through the SSL session with their customer.

This sort of service would not just be a so called "killer app", it would demonstrate the power of this new class of information tools to transform our way of life.