The tanks have something called "Single Destruction" now that goes on either 1 or both people who take the Double Destruction. We aren't yet sure how its allocated or why.
Umm...you're over thinking it. That's what players get when they soak the double destruction. No different than hard mode or even story mode. The only difference there is that it lasts longer on players, making sure to prevent the same players soaking a 2nd DD, which will happen if dps is slow.