According to Fightful Select, the original plan (as of last Friday) was to have “The Fiend” Bray Wyatt defeat Randy Orton at WrestleMania 37 before plans were changed to Orton going over. There were also no plans for any type of “gimmick” match (such as the “Firefly Funhouse”) or any sort of endgame feud for that matter.
The “surprise” finish was basically what we saw on Sunday night with Alexa Bliss appearing with “black ooze” (black ichor) dripping down her face to distract The Fiend long enough for Orton to drop him with an RKO. to end the match. Both Vince McMahon and Bruce Pritchard were said to be instrumental in having this decision being made for Orton to go over Wyatt, rather than the original plan.