Comment 9 for bug 168658

How about this dialog that lists the replaced fonts and gives the user the option to select all the affected objects.
With the objects selected the user has full control to do whatever they want
* Replace the font using the Text tool, or
* Highlight by setting the background / text color, or
* Highlight by using a Filter like Morphology->'Outline' that can be toggled on and off.

@gez, I like the proposal, but instead of a special font substitution highlight mode (that would need show/hide controls) if we select the objects, the user can do any kind of highlighting, deleting or replacing without a special mode.