Here's an suggestion, would be handy for us, not sure how many other folks have this problem:
Typically when we are having folks translate resources for L10N, they don't necessarily have access to or experience using Eclipse (so the plugin doesn't help). Instead, we provide them a spreadsheet with the message key, and a column for each language entry; they fill out the spreadsheet (in context with the application, of course :-), and we then create new .properties file(s) from the result.
Would be nice if we could use the RBE plugin to generate the spreadsheet automatically (preserving comments, order, etc.), as well as parsing it back into corresponding resource bundle(s).
I suppose one could support other formats (XML, CSV, etc.), but regardless of format, the key is the ability to combine on export the resources for each message in a single row/entry/etc. in the file, just as the RBE plugin does interactively, and be able to "burst" it back on import.