After posting some stuff the the microformats-discuss mailing list I had a fascinating off-list reply from Keith Alexander, suggesting that I look into eRDF (embeddable RDF) as an alternative to a new microformat (and not only because new ones seem never to get anywhere these days, and perhaps rightly so). The links he pointed at have really whetted my appetite. There are a couple of extra complications, at least from the point of view of keeping authoring as simple as possible (the need for link tags, for one), but it sorts out some of my concerns immediately and opens the "format" up to existing eRDF parsers. Perhaps if we were to come up with some recommended schemas and element sets for museum objects we could reach some sort of stability and with a little adaptation even the work I've already done on the Gathery might not be wasted, but as Keith pointed out, the data would also be available to Piggy Bank and more. Hmm, definitely one to pursue and I'm glad I exposed myself on the list, even if it does mean I drop the µƒ idea altogether.
More on eRDF: http://www.getsemantic.com/wiki/ERDF