I am pretty sure the "requirement" to go to interference engines is one of many design choices when attempting to meet all the needs of a modern power plant:

HP and torque curves
Emissions
Cost and lifetime maint costs
Fuel economy

Many companies have chosen to use timing chains again. BMW is moving to no cam shafts at all (air actuated valves controlled by computerized timing like in F1 cars) some time in the next 5-7 years.

I doubt ANY manufacturer would choose an interference design over a non-interference to increase the income of the dealer service departments *from which they receive not a dime) or the parts sales. The customer ill will would NEVER make this financially worthwhile.

Do you think GM intentionally chose a bad design of their 3.4L V6 so they could sell intake manifold gaskets? They made a (in hindsight) poor design compromise.