For example, about a year and a half ago (maybe a tad longer) Grow A Tog was rampant, and the deck Diamond Dallas was created which was Gro A Tog/Miracle Gro, with the Oath Engine sideboarded, thus creating 2 different decks out of one.
You mean Emerald Alice? Or were they beaten to it by a full year?
As far as transformational sideboarding with control decks is concerned, I think that enough decks have a catch-all plan against "Control" decks (that is decks with 4 Brainstorm, 4 Force of Will, 4 Mana Drain) that it mostly doesn't matter which flavor of control you are playing.
Perhaps within a different archetype this could still be employed. Nothing jumps out as obvious though.