After the Red Wedding was the attack on the Wall by the Magnar's infiltrators, Bran and company meeting Sam in the Nightfort and passing through the Black Gate, the siege of Mereen and the exposure of Jorah Mormont's treason, Joffrey's wedding & Sansa's escape, Jaime's return to Kingslanding and falling out with Tywin, the trial of Tyrion and the Red Viper's duel, Davos saving Edric Storm, Mance's attack on the Wall, Lysa & Petyr's wedding, Jon being sent to assassinate Mance Rayder and Stannis' arrival at the Wall, Jaime freeing Tyrion and the murder of Tywin, the Hound's fight with the Mountain's thugs, the election of Jon as Lord Commander, Arya getting a ship to Braavos (a minor event, but the payoff to the Jaquen H'gar bit with the coin), Petyr's murder of Lysa, and the epilogue where Catelyn's resurrection is exposed. That's way too much for one episode, and probably worthy of two or three.

I would guess, that if the penultimate episode ends with the Red Wedding, the finale will be people reacting to it, and maybe one other big event. Depending on how fast they have the other storylines take place (there is not a whole lot between what we saw in the opener and the Red Wedding, so unless they are going to spend seven more episodes arguing about how to placate Walder Frey, I think other episodes are going to advance the other storylines. The capital city storyline is way too busy to have Joffrey's wedding before that, and there is too much afterwards, with Tyrion's trial, the duel and his escape and murder of Tywin, and Sansa's post-wedding adventures. So I think a lot of Tyrion's ordeal might be pushed to next season, maybe even including Joffrey's wedding, though I kind of think Tyrion's arrest and Sansa's escape might be tempting cutoff points for season-ending cliffhangers.

It might have been better to accelerate things so the Red Wedding is earlier and have Joffrey's wedding as the penultimate climatic episode, with the trial, duel and Tyrion's and Sansa's escapes in the finale. There are so many ways they can handle this, speculation is kind of pointless, especially if we don't know what they've cut, or added in. They might not want to wait for two or three more seasons before bringing back the Greyjoys who were entirely unseen in SoS, so we might get a scene or two of Theon in captivity as part of the foreshadowing of the Boltons' treachery, and other types of things that stretch out the season. Look at how Robb's love interest was drawn out last year.