Looked into it. Not likely to be a feature. Widgets in glossary boxes would be ridiculously complex for the fact that it is not really necessary. The intent of a glossary entry is to be a simple definition. The fact that pictures and some formatting works there is a bonus, but as you have probably noticed, already has to go through some special logic and scrunching to get it to fit in a popover.

The widget system has a lot of rules and overhead bounding the widgets in a practical way to the natural thought surface … they are absolutely positioned entities … trying to squeeze all that into a little popver and still all work right in most cases would be as big a job as the whole widget system by itself. It’s just not necessary, only to get the point across for a glossary definition. What you can already do in a basic rich text editor is plenty. And if you really really want something in a glossary definition that you can only make with widgets, make it, snapshot it, and upload the image. As you say, you do that almost second nature already … and one hell of a lot easier than the weeks of programming, and debugging for all the browsers, it would take.