Tried this some time ago see:
the email discussion basically informed me ELDA's purity depended somehow on not returning anything not in the triple store. I still dont really get that.
Possibly many of your constructs can be rewritten manually as property chains - but note this wont handle any inbound references to the objects - easy to include in CONSTRUCT, or any manipulation to derive content.
Anyway for me the solution is largely through entailment of the graphs i need in the triple-store, using RDF4J and SPIN for example.
The other big ticket item is to be able to deconstruct variables in the request - for example extracting a namespace from a URI and running a query using that as a filter.
At this stage I'm waiting for a lightweight replacement that handles views, flexible constructors, and probably ignores optional properties aspect of queries.
Anybody got other implementations, or other APIs they think meet the goals of content-negotiation over multiple views?