This amounts to a real conversation now on this subject, with Phil Windley, Marc Canter, Bob Wyman, and now Pat Patterson chiming in:

Pat writes that in his experience, the dynamics between identity providers and relying parties may be quite complex:

...In the B2C world, it seems likely that the role of identity provider will naturally gravitate towards the big guys - maintaining a secure identity infrastructure is expensive - scale provides natural economies...

...On the other hand, in the B2B arena, the dynamics may turn out to be the reverse, as relying parties (service providers) ... may take the driving seat, implementing a range of protocols as they implement federation with a range of their customers.

Let's take this a step further. If user-centricity is really what we are after, it follows that I am my own identity provider in many circumstances, doesn't it? (Even if I let somebody else manage the server that runs the code and stores the data.) There seems to be a C2C model as well. What might the dynamics be there? That's the truly decentralized, peer-to-peer version of identity ...