I don't fantasy book as much as I used to, back when Punk was around I was all over it given how many times they disregarded him when us fans wouldn't have. But as of right now I'd love to book a (somewhat) 1 year story between the Shield guys leading up to their 2nd, and bigger, triple threat at Mania 35.
So I'd have Seth hold the IC title for a couple more months, making him look stronger after every defense he gets through while also making the matches more difficult for him to keep on retaining the title. Then, after a brutal and successful title defense on some PPV, the heel beats the shit out of Rollins because he's mad and all that, just so Dean Ambrose's music can hit to make the save. The heel runs off, Ambrose helps Rollins up but immediately takes him back down again with the dirty deeds, making it clear that he ain't anyone's lackey and that he's the definite #1 even after taking time off. I'd also state that I'd have Dean do all of that on the actual PPV rather than the Raw after, simply because it's nicer to have PPVs serve as checkpoints during a long build up.
So both of them have a feud over the IC title with Ambrose coming out on top at the end of it all. Not only do both of them have great in-ring chemistry but it would also be Dean Ambrose's moment to shine, given that he's never been able to play a heel during his singles run so far. Some little things he could play up to would be how he was always the one who successfully retained the tag titles for them by ending their matches with the dirty deeds and the 3 count whilst Seth is actually responsible for losing the titles after getting pinned by Sheamus, or even how Seth "replaced" him with a loser like Jason Jordan as soon as he got injured.
Anyways, looking at the timeline, if we're adding the time it would take for Ambrose to come back and have a feud with Rollins, we'd probably be around the beginning of 2019 which is the Rumble. Now that Seth is without the IC title he's turning his attention towards the Universal title which is being held by Reigns. Rollins goes on to win the Rumble, yet Ambrose now sits on the side with the IC title and wonders "why did I even go to battle with this dude just so he can move up the card regardless and I can stay in the midcard again?"
Kurt, or whoever's GM at that point, is announcing the Elimination Chamber where Reigns will defend his title against 5 other guys as per usual. Now Ambrose wants to be in that match, yet the GM wants Dean to defend his IC title at that show. Ambrose ain't having it and attacks the EC participants during their qualification matches on a weekly basis until the GM finally caves in and gives Ambrose the ultimatum of dropping the IC title to get added to the EC match. Dean obviously accepts, the IC title is now vacant but he gets his big shot in the EC match for the Universal title.
At Elimination Chamber it comes down to Reigns, Ambrose and some other dude (not really relevant). The 3rd guy gets eliminated by Reigns and Ambrose immediately rolls Roman up for the upset victory. Ambrose leaves Elimination Chamber as Universal Champion, Reigns is guaranteed a rematch and Rollins is the Rumble winner aynways. The stage is set, and the match is served on a silver plate.
As far as the match at Mania itself is concerned, it's probably not gonna main event given that WWE's already planning the Charlotte/Rousey angle for the main event spot. So it's ok to have a multi man world title match if it's not the main event of Mania. Ultimately I'd have the babyface Rumble winner Seth Rollins go over in the triple threat, because Ambrose already got to win their first triple threat and Reigns had a lengthy run with the Universal title beforehand. Also, more Rumble winners need to actually win their title matches at Mania, not like this year for example. Otherwise the Rumble's statistics of how many % of winners went on to become world champs at Mania will drop quickly as I'm pretty sure we're already at the 50% mark or smth
