Let us just say that the fullback position is the least of our worries. O'Davis is there for however long he is fit and willing - he is afterall still at Origin standard.
If and when O'Davis is injured and/or retires, you have Kurt Gidley who might play there depending on Hagan's thinking regarding new players at 5/8 (Witt, Dorn, Ennis etc).
Then you have the option of Hughes - although I question how long he will remain a First-Grade regular if others continue to pressure for positions. He is safe, but compared to others may be deemed no longer and automatic backline selection.
Then you have Michael Young - who is my book will have to get there eventually. He is the current P.L fullback, has some speed and agility and is sensible when under pressure - he is also only 19 so there is time for him to bulk up a bit and get some experience.
You've got Ennis, Witt and Dorn all still in the system somewhere, and a re-shuffle of the backline to pop any combination of people in various positions is possible. It all depends on Hagan's thinking.
My theory of the past 18 months or more has been:
O'Davis until he retires, then Michael Young for the future - I won't change from that, but perhaps there will be a phasing-in period depending on whether Hagan wants Young going straight to fullback on debut, or perhaps give him some experience in various positions from the bench.