Claims section supports key delegation. It's not a problem for many applications and users. Even though the design looks PKI- centric, but in practice it probably isn't going to be a problem. They're a real-world problem that SAML should solve. It's hard, but we're engineers.
Interoperability is the concern here.
At least hooks for sessions should be put into the spec. We don't have another year's worth of window to finish this. We should use future versions to add to SAML 1.0. A lot of terms can be removed. But the time constraint was real.