It's not a matter of being able to be brought up to speed. It's a matter of desiring to GM in the first place. Some people don't like the idea of GMing. There's got to be an innate desire there.
You can't just throw someone a book and say, "We want you to GM, so do it."
A person has to want to do it. Take Dodger for example, she expressed multiple times she wanted to, and then got the help to do it.