There definitely is a small niche market for this. It's for the significant others, and regular passengers of elderly pilots. Even if there's no actual statistics about fatal accidents resulting from pilot incapacitation, I know quite a few pilots and passengers thinking about this scenario.
A passenger who has had a little training in
- Calling for help (radio, transponder usage)
- Follow instructions (vectors)
- Land the plane in such a way that the occupants are not more sick than they already were
is far more likely to enjoy a flight, without the worry 'what would I do if'.
Plus such a course provides a fairly good basis for the pilot to slowly give the passenger more significant tasks in flying the plane.
If I had a non-pilot passenger who flew with me regularly, I would at some point suggest that he/she would do exactly such a course. Although I think the Fenland course, at 7 to 10 hours, is a bit too much. I would say one or two hours would be enough, initially.