There was a discussion on the email list about what the plan was here, but I'm blonde, and it's not entirely obvious what the conclusion was.
Option 1: No DTD, only normative Schema
This makes the most sense to me. Schema is not exceptionally more difficult to read than DTD, and tools support for it is widespread now. DTD is not easily digestable by XML toolsets for metadata transformations. This is especially important in MDA applications.
Option 2: Normative XML Schema, non-normative DTD
If we go this route, I believe that the DTD should be generated from the Schema. This is unfortunately difficult because Schema contains a couple of constructions that cannot be translated. Manual synchronization of the DTD to Schema is going to be prone to error, if it occurs at all.
Option 3: DTD only
I think this has already been eliminated.