This is indeed an interesting topic...
Essentially there are two ways to make certificates more adapted to their working environment:
1. Clobber certificates with more "stuff" to as the draft suggests
2. Use a mapping facility that maps a certificate into whatever is needed by the working environment
A major advantage with mapping is that you can use TTP-issued certificates (a.k.a. 100% outsourced PKI), and that the very same certificates can be used by multiple relying parties in many different environments.
A major disadvantage with mapping is that Microsoft and probably most others as well, do not yet support this fundamental capability except to a very limited extent. Contributing to that, is the fact that current PKI-standards do not offer the kind of manageble mapping support needed for efficient usage of TTP-issued certificates.
If Microsoft and others are to upgrade their PKI support (which both solutions require), I really hope that they settle for a mapping solution.
cheers, Anders