I have a flight on SK908 in about a weeks time to Oslo which is currently scheduled with new cabin.
But they don't lock it to an individual route, the new planes "move around" in the route network. And as more of them show up, that's likely to become more the case rather than less for a while, until you get to the point that the majority is upgraded.
Meh, correction, which proves the second paragraph. It had new cabin when I checked last night. It's back to old cabin now.