It would be a great fight, but I think if JDS wins against Struve convincingly he should be rematching Stipe.
Also Arlovski is a big step up for Ngannou!
Why rematch the champ after one fight against someone like Struve? Stipe should fight the Cain/Werdum winner. JDS needs at least one more win and Ngannou would be a good one if he can get by Arlovski.
I think if JDS wins against Struve convincingly he should be rematching Stipe.