I can definitely see that going Joshua's way, but slightly favor Fury. But the winner probably needs beat Usyk too, to get the WBO belt to go undisputed.
It's hard to see how Joshua wins after last night. The slimmed down version that beat Ruiz still gets caught and outboxed by 19st Fury and is highly unlikely to pose the KO threat of Wilder. A heavier AJ just doesn't have the speed or stamina to cope with last night's Fury. If Fury can come into fights at 6ft 9, 19st, still really mobile, still good stamina and actually with KO power then he can absolutely dominate the division.
Styles make fights and I think Fury is a great fighter and I was one of the ones who predicted he will stop Wilder. However styles make fights and whilst I foresee both Fury and AJ causing problems for each other I believe AJ will win the Battle of Britain for the Undisputed Heavyweight Championship when they fight.