In more ways than one.
First, and most obviously, we got to see Paul McGann as the Eighth Doctor in "The Night of the Doctor."
To see Paul back on screen as the Doctor, even if just for six minutes, is amazing, and he was absolutely incredible. Now we not only know the circumstances of Eight's regeneration, we've seen it. I don't know if I can put into words the significance of this. He has an official regeneration scene, and it is perfect. No Eight fan could ask for more. The return of the Sisterhood of Karn is also very exciting. But what really got me?
"Charley. C'rizz, Lucie, Tamsin, Molly. Friends, Companions I've known, I salute you."
Those are the names of his Companions from Big Finish Productions' Doctor Who audio plays. This is on-screen recognition of Big Finish. With the reciting of their names, those Companions, at least as far as I'm concerned, have become TV canon. Moffat talks about Night of the Doctor, and about Big Finish, in this interview.
But that's not all. Today the long-awaited trailer for "An Adventure in Space and Time" was finally released. It's a docu-drama about the very beginnings of Doctor Who, written by Mark Gatiss. It's coming out on the 21st of November and looks to be excellent.
Why is this so significant? Lalla played Companion Romana II alongside Tom's Doctor from 1979 to 1981. They married in 1980, and split 16 months later. As far as I know, they have not seen each other since the divorce. It's been generally understood that Lalla won't work with Tom – she hasn't, for example, recorded any DVD commentary with him. So this is big.
All of this is big. And I think I should be commended for writing something so calm when I'm still in a state of complete emotional turmoil from Night of the Doctor.
ETA: Big Finish is having a sale on some of Eight's audios, for anyone interested.