The dcxyz (or dcx) schema is an extreme case (but is apparently in demand).  I think the intent is that a client may silently ignore any elements from a namespace that it doesn't recognize. Granted, this doesn't much aid interoperability.  And another intent is that it be used with prior agreement of which namespaces are to be used. Again, not great for interoperability.  So the broad utility of this schema is limited.

I am certainly happy to create and support additional more specific schemas as requested.  But they need to be requested.

For example, 'dc+prism'.   That schema would be created simply by replacing

<xs:any namespace="##any" .....

with

<xs:any namespace="http://prismstandard.org/namespaces/1.2/basic/ "......

 

However, suppose someone then wants to combine dc, prism, and mods elements.   Create  a dc+mods+prism?   And so on. This is the sort of question we've wrestled with for the past 15 years (beginning with Z39.50).  I think the answer is, yes, we'll create a dc+mods+prism schema, only if a real business case is made.  What I resist is the suggestion to take the Z39.50 approach to dynamic schemas (i.e. element specification parameter).