I like it and haven't seen it suggested before. Nice job.
My gut is telling me that they're going to just go through with Roman Reigns challenging Triple H and beat people over the head with it. Now that he's officially retired, I can see them trying to get the babyface love for Bryan onto Reigns by having Bryan "endorse" and perhaps even "train" him for the match. They clearly want Reigns to be the long-term babyface for the champion, and I think they're just too stubborn to abort it.
Dean Ambrose would be the most immediately over option. Watching clips from RAW this week, Ambrose didn't look out of place interacting with Brock Lesnar. I can see them abandoning the Brock vs. Bray plans and have Bray vs. Taker, Ambrose vs. Lesnar and Triple H vs. Reigns.
A third option is that they have Ambrose win the match at Fastlane (where he will be the fan favorite) and go on to face Triple H. Reigns can then face Taker and Bray can face Brock.
I think your top matches are a configuration of Triple H, Roman Reigns, Brock Lesnar, Dean Ambrose, The Undertaker and Bray Wyatt -- and you can basically fit them together however you like.