It took me a little while to figure out why this question seemed so weird. Taking another look at the Workflow cleared it up for me.
According to the Workflow, here's how something ends up in Someday / Maybe: Stuff -> Inbox -> What is it? -> Is it Actionable? -> No -> Someday/Maybe.
Which is to say: The only things that end up in Someday/Maybe are things that are not actionable, according to the Workflow. So there really isn't any point of application for the 2-Minute Rule.