Idk what to think, but I love this idea :D I want it to be all-flashback! I read that Spencer and Ali will have scenes together, and I'm wondering..maybe Spencer knew something all this time? Maybe she forgot about it?
I agree. I think there will be a lot of flashbacks, like most of the episode, but it will have to end in the present to set up for season 5. Or, actually, they could show us something super shocking in a flashback that makes us realize how important season 5 will be. That would be extremely interesting, if they build up to it.
I imagine the episode will center around the 4 liars, Ali, and maybe a few others, all together finally, having a conversation about that night, or that summer even, and piecing it all together.
There are actors in the episode, that don't belong to the past, but the present, so it'll probably have a lot of flashbacks, but I doubt it's an all-flashback episode, even though it would be fantastic. If they'd end it with showing who killed Ali than that would be great. But that episode is for the Liars to find answers, If it's an all flashback, than they still don't know who killed her, even though the viewers may do (do you get what I mean?), since they only seek answers in the present and not past.
What I mean is, that whatever happens in that episode leads into Season 5 Premiere. But when it's an all flashback episode, the Liars are still at the same point they were before, since THEY still don't know who killed Ali. I doubt they would do that. They want to let the Liars find out the same time we do.