Instead of a ring system, I wonder if an ice body wandered within its Roche limit and was shredded and is spiralling around the planet rather than forming a stable ring system. Over the two years that the two images of Fomalhaut b was taken, it grew 1.5 times dimmer. It would be unusual for a ring system to go from face on to edge on, like a spinning coin, over just two years where the orbit of the planet is around 872 years. The ring systems in our solar system don't spin about the home planet this fast. The change from edge on to face on more often corelates with the yearly orbit if at all. But something ripped up by getting too close to the planet might leave a spiral of debries about the planet that may later either fall into the planet or form a ring system. More looks at the planet might discover whether dimming and brightening follow a regular pattern of rhythm.