Gilmoy: <12.Rae1> is actually a clearance tempo for the <bishop thing 13.Bb1>, an ideal post for a K-side attack. The LSB never moves again, yet combines perfectly with <15.Qd3> to threaten the Q entry, which goads Black to wreck his own K-side.
13.(or even 12).Bc2 would be slightly inferior because it mildly congests the d1-b3 diagonal, and Black's <27..d3> would "put the question" to it, costing another tempo. Instead, White insidiously uses <10..e5 12..exd4> as two free tempi for the pawn, and never bothers to recapture -- it's not worth a tempo!
This line has the feel of a rapid gambit, i.e. known to be "unsound", and therefore good enough to spring OTB on short time. Aronian (and many other GMs? excluding Ding, alas) might have already analyzed it to a draw, and figured that a super-GM could find the draw OTB with a 1-hour long think, so it's not worth trying in classical. Then he holds it up his sleeve and waits for a short game that matters.
Topalov once did it to him with that Nxf7 sac (which was duly refuted later that same evening!), so Aronian surely appreciates that it's not easy to remain calm OTB against the other guy's home-prepped ambush smirk. Ding seems especially vulnerable to this because he's not afraid to fight back with his own crazy moves, until he's completely wrecked.