Instancing could also help Xara push XX/XXP as a serious forms design tool, where a single copy of common elements, such as address blocks, corporate logos etc could be updated once, then automatically replicated throughout each form in the form-pack document.

Could be even more powerful if documents could link to an external symbol stored in a separate Xara file?

This is how applications like PlanetPress, Create!Form and FormScape manage instancing - i.e. along similar lines to flash.