Is this a good idea? Assuming you are targeting a global mass market audience, how do you pick which strategies to use? Or do you just use all on the list? Has anyone created a best practice login UI for such a use case?
"Global mass market" meaning? try to have a more focused definition for your audience. It all depends on the audience in general. For example, if you're making an e-commerce site, you wouldn't want to limit it to just folks who have a twitter/facebook account...but then again that depends on what you're selling. If however you were making some sort of a social app that leverages people's connections already, then there's really no need to use any other authentication strategy than OAUTH. So I'd say think about your target audience and make your decision.