In this case, it sounds very much like another database that I built back when I was teaching logic. There — as in math and other related fields — there was often something like a proof or process that students needed to show. So I’d have an “ideal” answer key but would need to be alert to other solutions, partial credit, etc. I liked to keep a database of questions so that I could offer instant make-up exams made of questions that were variations on the same basic set of skill-themes.
Still it seems that the format of questions can vary so much!
I recall that in that database I had lots of diagram-oriented questions. Having something like an illustration or graphic field will be helpful for people in many fields. Of course, more fine-grained diagram needs would be field-specific (I set up a venn-diagram-module for my logic teaching, for example). Still, for a basic showcase-edition to show the power of TiddlyWiki for teaching, it would be ideal to be able to help people see how exam questions can incorporate graphics.
Of course, we might then have a particular challenge to Charlie’s ideal (have everything for a question so neatly bundled into one tiddler that the parts wouldn’t easily be separated).
In fact, this application makes me wonder whether anyone has ever modified TiddlyWiki so that a particular named field (perhaps one whose name itself encodes the type of image — such as jpg or png) could store image data, the way the text field does for tiddlers whose type is image/png (or whatever)… (This would presumably be limited to one such image per tiddler. But that’s often exactly what’s needed!)