I'm not sure what % of people would be using a Metastore server as opposed to just using a local metastore - I know we have a usecase where we do want a centralized metastore server because it'd be the common metastore across multiple projects/processes and we'd like to add in monitoring instrumentation for it.
That said, if we were to use a -D parameter to determine the port, and apply jmx instrumentation in the Metastore server, even local clients should be able to make use of that change. Also, once we have a way to add in instrumentation, I suspect we should be able to add in instrumentation from a query level as well if needed. -Sushanth