To the anti-MMORPG people, ,this idea may make you happy
3 different classes, pure PVP type game, Feruchemist vs Allomancer vs Inquisitor
If you don't mind the fallout of the story and just enjoy blowing people apart it would be hella fun. This way everyone could be happy, and the strengths/weaknesses of each class would play into it (although you'd have to wait for HoA to make the Inquisitors) Allomancers needing metals, Feruchemists needing to store stuff (sped up of course) and Inquisitors needing what they need + rest after each battle. Pure PVP type game. Allomancers could only have a limited supply of metals in battle, Feruchemists only being able to store so much of all attributes, and Inquisitors just as they are. You'd have to incorporate a level system, each level having a different PVP arena and supply of metals/attributes/Inquisitor stuff.
For the iron/steel thing I think it should be like the targeting system in Advent Rising. Flick that way select that line go, flick another go that way, and holding a certain button for a certain length determines the distance. Flick+the button while "flying" through the air to grab onto something else metal, with the solidity of the line determining whether or not it will hold you. I would enjoy either an RPG, MMORPG or a Morrowind type game. I think the ability to move around the environment as you will would make it a GREAT game. Doing whatever you want would be AWESOME!!! I think an Assassins Creed type with the targeting for steel/iron from Advent Rising with the freedom of environmental action would make it perfect. It would have to be on PC or an EXTREMELY complicated control setup for console. The downfall with PC would the be movement. I've only played WoW form my MMORPG experience and if it was similar to that it would fail.
That's my take