On Requirement 3.8 (Bookmarkable Queries)

On Requirement 3.8 (Bookmarkable Queries), cf.
http://www.w3.org/TR/2004/WD-rdf-dawg-uc-20040602/#r3.8 ,
a question of clarification:
Does "express as a URI" means a new class of URIs will
be created? Or does it rather mean "embeddable in a URI"

Obviously the first interpretation (esp. as a MUST) is
rather demanding. In the case of the first interpretation,
given the costs of creating a new URI scheme, what is
the rationale/benefit of going with the new URI scheme
rather than with the classic container approach?

Thanks,
-M