Microformats, while a relatively young movement, are an outgrowth of a movement that’s been going on for quite a bit longer. For years now, web developers and designers have been abandoning purely presentational markup in favor of structural markup. As you move away from presentational markup and towards cleaner, more meaningful markup, you open up the possiblity of having not only human semantics, but also machine semantics, which though they are two different things, can often be very similar (see the wikipedia for more on this difference).
Anyway, microformats make the most sense in this context, where we assume that web developers are somewhat concerned with semantic markup and have already gone through the steps of making their markup meaningful.
In essence, Chris was asking for a microformat for a use-case that doesn’t quite exist yet (at least for a majority of Web users). Of course, Chris is just gonna go off and invent that use case, which is great, but just not a case for a new microformat. Part of the idea behind microformats is to standardize and codify emergent, popular behavior on the Web. If some useage of the web is too nascent to have converged, we can’t easily codify it, so we choose to pass on the problem.
However, just because Chris’s use case wasn’t appropriate for developing a new microformat, doesn’t mean he can’t use preexisting microformats and his own idiomatic semantic markup. In fact, he really should, because if his project catches on, then we may want to create a new microformat in the future, at which time his work will be great prior art.
Of course, the appropriate cliché here, would be “paving the cowpaths.