I know they're getting rid of hold luggage to save money on turn around times and baggage handling fees as said in the article, but there must be some other money making idea Ryanair can bring in to make use of the hold when there is no luggage in it.
Cargo adversely impacts on turnaround times, and when your business model is built on tight turnarounds and high utilisation, you don't go looking for things to risk it.