The Obamas returning to politics is a liberal fantasy at this point. Michelle has never hidden her lack of enthusiasm for that life, which I think only fuels the fantasy, and I doubt Barack would want to put himself through that ringer again, even as an administration member. Imagine that Senate approval process- what a nightmare that would be to go through for him.
I don't believe a former president has ever served in a successor's administration in a formal capacity. The closest I can think of is Taft joining the Supreme Court.
"...everyone finally shut up, and the audience could enjoy the beginning of the Anatevka Pogram in peace."