Therefore, NI proposes that a new requirement be considered by this group: "The query language shall have an XQuery compatible concrete language syntax."
I don't think you could make a more premature proposal. The DAWG is trying to avoid syntax issues, preferring to get the semantics right first --- a good idea. To be proposing concrete syntax requirements at this stage is surely jumping the gun. I am even more surprised to see a proposal to mandate as poor a prima-facie case as XQuery.
XML has a document centric, single-rooted, hierachial view of its data; and XQuery reflects that. RDF on the other hand is a open-world, non-rooted, cyclic directional graph-based view. It is not immediately obvious how to reconcile these two approaches; neither is it apparent that a syntax designed to query the former, will be appropriate for the latter. This becomes particularly apparent when you look at the block-and-layer diagram in Jeff's proposal pdf. The only link between the XQ Data Model, and the RDF Triples is that both are sometimes serialised as XML --- ok XML tends to be serialised as XML, but lets not quibble, RDF often isn't.
On the other hand, XQuery is itself quite a nice solution to its problem. Particularly nice is its definition of two isomorphic concrete grammars sharing a common semantic model. I would have absolutely not problem with discovering that XQuery can be married with the semantics required by an RDF query language, in fact that would be great. Still I would like to see the DAWG finalise the required semantics first.
I would be concerned if XQuery was even considered desirable at this stage, let alone a requirement.