Ensuring high quality sources where needed, especially science/academic topics (narrow focus)
I'm as sympathetic as anyone to the idea that "not everyone can be a helpful editor". But I think making people go through a 15 minute workshop just to create an account is a bad idea. It's far too restrictive. Anyone in business will tell you that you don't want to create hurdles at the signup stage. You want to get them in the door, enjoying whatever it is you have to offer, as quickly as possible.
A *voluntary* workshop is a good idea though. Even a workshop that could be required to go from "average editor" to "editor who has the power to participate in more serious work" -- like working on featured articles, or creating new articles. That's worth discussing too.
But we can't screw up the experience for the first 15 minutes. That's the most critical moment for getting a volunteer's support.