#2 A steel cage encloses the participants inside the ring
We saw the Rumble go hardcore during the 2001 edition when wrestlers such as Raven, Perry Saturn, Steve Blackman, and Al Snow introduced chairs, kendo sticks, and garbage cans into the match. We’ve also seen a ladder, surprisingly, as R-Truth mistook the over-the-top-rope match for Money in the Bank back in 2016.
What we’ve never seen is a steel cage being used in a Royal Rumble match.
For this to come into play, there would have to be a steel cage match earlier in the evening, lest it be obvious that it could somehow, for some reason, become a part of the Rumble match at the end of the night.
During the Rumble, an underhanded superstar (such as Baron Corbin or Seth Rollins) could be close to being eliminated by a fan favourite (Roman Reigns or Braun Strowman, for example). The devious wrestler would call for the cage to lower, thus protecting them from elimination. It would take very well-practiced timing to pull off without coming off as extremely contrived, but if they could pull it off, it would be a heck of a moment.
One way to win a steel cage match is by escaping the structure, but if it were to lower to the ring during the Royal Rumble match, wrestlers would be trying to stay inside the structure, creating the opportunity for all manners of unique spots and situations.
The cage wouldn’t stay lowered for the entire match, as the novelty would grow old and make it essentially impossible for the match to end, but even if just for a few minutes, the sight of a steel cage in the Rumble would be something talked about for many years to come.