Neo4j 1.2 Milestone 2 has been released!
Relevant to topic maps in general and TMQL in particular, are the improvement to indexing and querying capabilities.
Neo4j uses Lucene as a back-end.
Would Neo4j be a good way to proto-type proposals for TMQL?
To evaluate concerns about implementation difficulties.
And quite possibly to encourage the non-invention of new query syntaxes.
A side effect would be demonstrating that Neo4j could be used as a topic map platform.