One of the things I feel is missing from most MMOs is verticality. More often than not MMOs keep us grounded - even the ones with flying mounts do this. I can't really scale walls, parkouring up a mountainside is a series of well placed jumps up otherwise unscalable terrain. Even when we take to the skies in a flying mount, it feels less like I'm no longer tethered to the world below, but rather I'm just on my normal horse...just airborne.
If I could take any mechanic from any MMO, it would be the movement and verticality offered by the movement from Swords of Legends Online and inject it into a game like Guild Wars 2 or even Final Fantasy XIV. Imagine the hallmark of a Monk in the latter title being that they can easily scale walls, adding some more flair to the class.
Naturally this wouldn't work in most MMOs. I cant imagine a class or mechanic like this in The Lord of the Rings Online, for example. It doesn't fit the world very well, so to speak. New World might not necessarily make it work either, especially when you consider how obselete it would make defending the settlement's fort - especially if your enemies could easily hop over the wall.
Another mechanic I'd love to steal is LotRO's legendary weapon mechanic. We sort of saw a form of this in World of Warcraft Legion's artifact weapons. I'd love to see more games set you on a path to create the perfect, bespoke weapon you use and grow with over the course of the MMO, though. Instead of constantly grinding for more gear, give me the ability to not only craft my own weapon, but furnish it how I'd like through injecting stats and modifiers into the weapon, but then give me the ability to further hone, refine and reimagine the weapon over the course of the next 20-30 levels , taking me through endgame. It's something I wished more MMOs would do. As much as I love the genre, I despise the grind sometimes - make the grind more personal and meaningful by not forcing me to look for a new item altogether, but instead improve one I've honed over countless hours of gameplay, making it my own.
What about you - is there a mechanic you'd love to steal from another game - MMO or otherwise - and inject into your favorite MMO? What is it and why?