9. Is This Arcadia?
We've only got a few lines in odd Eccleston and Tennant episodes when it comes to the big battles of the Time War, including things like the "Nightmare Child" and the Neil Gaiman-esque "Could've Been King with his army of Meanwhiles and Never-weres". One of the battles itself we did hear of is Arcadia which Tennant mentions in the episode 'Doomsday'.
"I was there at the fall of Arcadia. Someday I might even come to terms with that." Maybe nothing more will come of it than a big action set piece, but it would be nice to definitely see some of the things the Doctor talks about in the previous episodes. Doubly so when he mentions being there himself and triply so considering Tennant says it and he's returning for some timeline confusing antics alongside Matt Smith. Perhaps Arcadia was like our Ground Zero?