Apocalypse has been retracked fairly extensively, and it's much better than is has been. Still not perfect by any means, but better. Not long after the retracking, I had a few surprisingly good rides on it, especially at night... it was almost like it had just opened. Since then, it's gotten bummpy again, but nothing like it was (except for those last turns, but you're mostly already slowing down by then). I've heard absolutely nothing about new trains. It already has millenium flyers... what else would even be a viable alternative?
I've heard elsewhere, and then confirmed for myself, that the "secret" seat on Viper is 2nd from the back. Strangely enough, it's the smoothest. I have no idea why, as it goes against everything you'd expect from Arrow... but it does somehow work for this ride.