To put it in plain words, 'shifting' is a kind of fashionable complex. Especially in certain game communities, likewise in settings for fan fictions and discussions. It is basically about transitioning or "shifting" your awareness from the current reality to another one, usually in relation back to your favorite fictional universe.
Just think you might have breakfast at the Shire or help Naruto in a desperate battle against the Akatsuki. Cool, huh?