I think that in the era of GaaS and batlle passes, the time limited in-game events will become more and more frequents. Maybe not only getting exclusive cosmetic backgrounds or loot and unlocables, but also to get exclusive story bits and missions that you may miss if not playing during that period.
Other than that, I think the next fad (or trend) will be AI generated procedural side quests or conversations with random NPCs, but I think won't see it until a few years in the future.
Also, in a few years in the future, once they mastered next gen engines like UE5 we may also see more procedural environment destruction that affects gameplay in a more natural way than in the currently, canned one: instead of being able to break that specific part of the wall designed to do it, or being able to destroy only that bridge / floor / ceiling prepared to do so, to give more flexibility (something hard to do because it could break level and mission design).
Fad? No way, man. Grappling hook, if used correctly, is one of the most mechanics in a game.
Returnal is probably the best example and use case of a grappling hook.
Yeah, grappling hook (somthing that existed since the '80s in games like Bionic Commando) when well implemented is very cool. I also think that it has been a great addition in Halo Infinite.
Inspector Gadget style personal helicopters. Trust me on this.
Also, BotW style personal gliders ccame after grappling hooks (which really saw a resurgence with JC 2 in the mid to late 2000s.)
I see both as cosmetic variations of the typical jetpack, seen since the 80s in many games, in 3D games the oldest I remember is Duke Nukem 3D. Or as other similar gliding gameplay mechanics we saw since the 80s. Or more recently, in 3D in many games like Sonic Adventure, Little Big Planet 2 (Nintendo loves to get ideas from LBP), Batman Arkham, Assassin's Creed 2, Just Cause etc.