Versioning the specification

We need to figure out how the specification is going to be developed now that we ratified version 1 of the provisional spec. At some point, we'll need to release a non-provisional v1, backed by the CTS coverage of some implementations. But then we'll still keep discovering new limitations, potentially, especially in D3D12, which we don't have as clear of an idea about, at this point. The existing structures are set in stone after v1, and we'll have to add new structures.

Are we going to make it a version 2 of the same specification, with new structures in it? Is it even valid to add new types/structures to later versions of a spec, as long as backwards compatibility is preserved? cc @dgkoch

Review the existing provisional v1 specification, its structures, and the CTS coverage of implementations, with particular attention to the unresolved D3D12 limitations. Resolve whether later additions should use a new specification version while preserving backwards compatibility, then document the agreed versioning approach.

Written by the indexing model from the issue text.