I can see this working really well for a Superhero game. I love the idea of playing with the heroes' reputations and forcing them to balance their activities with public perceptions. The prospect of a hero having to avoid law enforcement and other "good guys" as a result of their own in-game screw ups sounds quite promising. I'm going to keep this in mind if I ever run a Superhero game. I also agree, the specific Mistborn magic system could really easily be tweaked to support classic super-heroics.
I was thinking about trying a star wars adaptation. I think it would work pretty well.
Ooh. That actually sounds like a relatively easy conversion. Attributes, Standings, and Resiliences can pretty much stay as they are, though the flavor of Spirit can shift. The only thing that seems to need tweaking is the powers system, but even that could be relatively straightforward ... a lot of the things Force Powers can do are already built into various metals so there's a lot of reference for how to stat damage on, for example, a Force-pushed crate. Emotional Allomancy is a lot weaker than Jedi Mind powers, but the sorts of things that typical Brass/Zinc users can do are of similar strength to Obi-Wan's small mind tricks in A New Hope so it still provides a nice stating baseline.
I see two main approaches here. 1) There is a single Force rating, and stunts do all the heavy lifting in differentiating Force abilities. 2) A Force breakdown sort of like what we've seen in a lot of the Star Wars video games--Jedi Knight had Push, Pull, Speed, Jump, and so forth. You could write up a similar list to your taste and either throw in an additional skill for miscellaneous uses of raw Force powers or just reduce the dice pool of one of the other abilities when it is applied in a way that requires fudging.
The trouble I've run into with my supernatural game is finding something else to do with Standings. Resources, Influence and Spirit don't quite fit into my design. Players have a well understood ability to obtain equipment and resources via the RCMP and won't be experiencing enough political intrigue for them to spend resources on being influential. My current solution, is to break the Physical, Social, and Mental realms into a Power and a Control rather than Attribute and Standing. Something like Might/Presence/Reason and Agility/Savvy/Wits. I'm still tweaking the breakdown between them, but I feel like this approach allows me to keep a the most effective parts of Mistborn's character system while simply shifting the scale of the game to focus on the characters' here and now. It also means I can still sensibly add the two together for calculating resiliences.
I believe I've figured out a nice alternative magic system as well. For the purposes of character creation, it's a third score block that contains (working names) Influence, Knowledge and Connection. Influence is your power rating--how much of a supernatural punch you have. Knowledge is how much the character knows about supernatural mythos, religious traditions, and so forth--it doesn't necessarily represent what the character knows to be true, just how much total supernatural data the character has. High Knowledge can represent an unbelieving scholar who happens to uncover the "true" versions of the supernatural topics she studies without believing them. Connection is how receptive to the supernatural a character is. A high connection can represent significant supernatural belief/superstition, a strong supernatural radar and/or the ability to perceive the supernatural without becoming mentally unstable.
All three can be "spent" in much the same way Standings are spent in Mistborn. They're used, respectively, to alter reality**, remember useful supernatural detail, and gain significant supernatural understanding of a situation. Characters need to recover their powers, do additional research, and re-attune themselves during breathers to be perpetually using these abilities. These can be increased or decreased during play as well if, for example, a character with a low Knowledge has a long chat with a sorcerer who gives the character the supernatural low-down or comes across the Necronomicon.
**Influence has two uses. First, it is the number of points allocated for buying supernatural powers. Your Influence score, however, is also a sort of Standing just like Knowledge and Connection. Spending Influence is not a direct use of purchased powers, rather it is a blunt, granular use of power that allows for things similar to catching a lucky break, or at high levels, performing feats of power that would normally require a purchased power. A high influence can let a powerful Telepath temporarily summon a poorly controlled blast of fire.