I'm onboard. A ways back I started writing a desktop application for RM2 (see http://www.jediwars.com/RMEC/) that saved all its data in XML files. I was trying to design so that every piece of data was configurable. There was going to be an XML file for your SpellLists, Skills, Stats, Races, Languages, Professions, etc. Then there'd be a separate XML file for your "campaign" which combined everything, and a separate file for each "character". I was going to try to have available all the chargen options from the various Companions and then you would indicate which rules were used in your campaign, effectively enabling/disabling various features of the app.
I've been itching to pick this back up, but been thinking about writing it in Flex instead of Delphi (well, since I need some experience in Flex), but the client app doesn't really matter. What's important is how the files are created. I'd very much like to have the XML files follow a community-agreed standard. This would be for RM2/RMC though, not RMSS.
Has anyone pieced together a group for determining Schemas? I'd be willing to donate my time as well as some xmlDraft licenses (xmlDraft, the Smart XSD Editor http://www.sysonyx.com/xml-schema-editor) if it'd make creating the schemas any easier (I'd prefer to not use DTDs).
-shnar