Stefan Brands has pubished a Primer on User Identification which can be downloaded here. It is a good introduction to Stefan's thinking and research – very stimulating work.
I know there are people who hear about a metasystem proposal and think, “Can't we just stick with TOKEN-X and have done with it?” And I understand that as a human reaction. But I urge people to look at systems like Stefan's- and the other innovative systems coming from other “identity innovator” colleagues. These systems are being built today. Each of them has characteristics that are ideally suited to various contexts. Let's make sure, as we build an identity infrastructure encompassing a few billion computers, that it will support these innovative ideas.