i do agree - i just doubt trix/rxr/n3/turtle will get widespread adoption (one can hope though) - trix and rxr mainly because of the 'overly' verbose syntax (yes i thought of entities here) and n3/turtle because it's simply new and people prefer to reuse their existing knowledge (even when they *should* be willing to learn new things, like in this case). one would need to prove that the use of rdf/xml is generally more harmful than your proposed way, and get acceptance for it (the harder part).
for xml to triples - what about a new transformation reference with xslt in the background? something along < ?rdf-transformation type="text/xsl" href="http://example.org/stylesheet"?>