The GOLD ontology is missing some concepts (features and properties) for some (maybe many) languages, but the process for extending it is somewhat defined. There is e.g. a Google group where issues can be discussed:
http://groups.google.hr/group/gold-ontology
Indeed, one good idea would be to have axioms and concepts getting into GOLD, to extend its usability for a wider range of scenarios and research questions. The comparisons you mention would be exactly what we would like to see, e.g. some sort of typology of languages via individual instantiations of GOLD (for the qualitative comparison, and qualitative cross-dependencies between features), as well as via annotated corpora for quantitative differences and similarities.
We used the GOLD Ontology in our morphological parser for Croatian (CroMo), and we looked somewhat at the possibility to map it to other common tagsets. Our goal was exactly this, being able to run qualitative and quantitative similarity measures across languages and corpora via some general tagset (and mappings of others to this one, so that we can use existing corpora).
Mapping of e.g. MULTEXT (EAST) is somewhat possible (maybe somewhere loosing specific properties that GOLD would have, but MULTEXT not etc.
ciao DC
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