I featured a U/R Control deck with Torrential Gearhulk in this space two weeks ago, and since then, the idea of the giant Snapcaster Mage in Modern has become more appealing. Modern is slowing down right now and that means there's room for some expensive, powerful spells to appear in maindecks whereas before they would've been a liability too often. Torrential Gearhulk has a lot of positive attributes that make it appropriate for those slots.
One, the body matches up quite well against a lot of threats in Modern. It's as big as or bigger than most Tarmogoyfs and trumps Tasigur, the Golden Fang; Gurmag Angler; Thought-Knot Seer; and Reality Smasher, all of which are tough to answer with a removal suite consisting of Abrupt Decay and Fatal Push.
Two, it dodges a lot of removal in Modern. Terminate is down in numbers, so Path to Exile is all that really remains to answer it efficiently, so you can be confident that it won't be a tempo sink too often.
And last, from a strategic point of view, it serves an important purpose for a control deck: gaining traction. Modern being such a large format with a variety of threats to answer means that control decks like this will nearly always be on the back foot early. That means you have to find a spot to turn the corner and become the aggressor, since Modern decks are powerful enough to withstand any amount of disruption given enough time. Torrential Gearhulk, as a flash threat, gives you the flexibility to pick your spot on a turn where your opponent doesn't do anything threatening and turn the game around in an instant.
The one missing component is an instant-speed card draw spell, even something as simple as Thought Scour, so you can cast your Torrential Gearhulks and Snapcaster Mages proactively when your opponent stumbles.
Unsurprisingly, the rest of the deck is typical control fare. We all know how good the discard, removal, and counterspells are and there's no reason to mess around with the cards that have been winning tournaments for years now. But supporting those cards with a new, unexpected, powerful win condition is exactly the kind of innovation that makes you say, “Why didn't I think of that?”