This is definitely a kick in the teeth to Airbus who would have enjoyed the free advertising and endorsement from one of the world's premier carriers. The cancellation was apparently due to some issues with the cabin installation and ongoing delivery delays. Or, as Qatar diplomatically put it: 

"The delays are … due to certain issues affecting the interior of the cabin which were identified during the airline’s standard aircraft delivery process, which includes rigorous inspections by its specialist technical team."

That's the airline PR equivalent of "we're taking our ball and we're going home."