Brandon Sanderson
In Mistborn Prime, there were no such thing as Mistings. Allomancy's practitioners were called Mistborn, and they could use all of the various abilities, depending on which metal they ingested.
When I started work on this incarnation of the book, however, I felt that I wanted to involve a specialized team of Allomancers. That meant including people who were really good at one specific thing, but who couldn't do other things. It's a staple of the heist genre–you want specialists. So, I split up Allomancy, allowing lesser Allomancers to exist. These people, who only could do one of the many Allomantic powers, would be very good at the one thing they do. And, since Mistborn were so rare, you couldn't really make an entire team of them. You'd be lucky to even get one. (Though Kelsier's team just got a second one.)
Soon, you'll get to meet the rest of the crew, and will be able to see how I split up Allomancy. One thing of interest, however, is that there was no emotional Allomancy in Mistborn Prime. I added Soothing and Rioting–the ability to make people less or more emotional–into this book because I felt I needed something that would be more. . .sneaky. These are skills that don't relate to fighting, and I think they'd be very helpful for the sort of political intrigue I want to do in this book.