Warning: Contains spoilers, theories, and possible insanity.
I'm not sure how much impact the story of Pink Floyd's "The Wall" may have had on the series.. so this is largely conjecture and coincidence. But, from the moment I saw ol' colossal titan peek his head over the wall, it reminded me of the time I saw the live performance of The Wall on tv as a child. The songs on the album gradually tell a story (yes, there's a story) about a boy-turned-rocker who gradually isolates himself from society by "building a wall". The 3-part song "Another brick in the wall" represents key points that drive him to isolate himself.. losing his father in the war (part 1), his schooling (part 2), and his failed marriage later (part 3). As the wall was gradually build through the performance, I vaguely remember stuffed or inflatable "creatures" peeking over the completed foam-brick wall, which set the memory.
I know people have made some of these connections.. there's a shirt that spoofs the album cover with a Wall Titan peeking through the cracks, someone put Annie's last fight to Another Brick in The Wall Part 3 on youtube, and likely others.
I'll focus on the points that seem to link up, and ones that point to a likely future and twist. Part 1: the lines "Daddy's gone across the ocean, leaving just a memory." and "Dad, what'd ya leave behind for me!?" seems to line up with the distorted memories, the key, and the basement. While Grisha might not be dead, he's clearly gone and left something for him (a "memory" or rather "their memories").
As the album's isolation builds, the character becomes delusional and believes himself to be leading a facist group, before feeling guilty and placing himself on trial (in his head), and is ordered to "tear down the wall" and open himself back up to society. A hidden piece of music on the first and last tracks hints at a cycle.
So in this one.. it's got more to do with how humanity walled itself off from the world and themselves. I can see Eren manifesting the "Coordinate" to rally the people as well as some titans.
It was theorized that he might be able to "order" people around.. and I think he may have even unconciously done this to Mikasa when he told her to "fight!" as a child (note the "electricity") This order possibly making her into a fighting machine in the style of the "live!" command in Code Geass, which forced Suzaku to survive by escaping or pushing past his limits.
When Eren is freed, and he begins to control his power, I can see him uniting humanity in a "titan purge". Leading people to slaughter the titans, maybe even making them into near-perfect killing machines. They begin a long and bloody fight to Shiganshina district. In the basement he discovers a twist, either Titans were once human (likely) and that they can still be saved, meaning he's lead a slaughter on humans he could have saved. Or (maybe) that humanity is walled the heck in because we were the real monsters (obligatory "man is the real monster" twist). Either way.. mirroring the character Pink in his "uniform" lets out an all-freezing "STOP!" to human and titan alike, and wondering "Have I been guilty all this time?".
This stop sets the stage for The Trial from the song, maybe externally in the story between Eren, his friends, perhaps even his father and/or the Ape Titan.. one of them will play the role of the judge. These characters could also be internalizations in Eren's memory too, if the trial is in his head. Either in hope that humans could become less of a threat, Eren or the Ape de-aggros the standard titans, or that there is a cure, Eren coordinates the Wall Titans to "Tear down the wall!" In doing so, mankind is able to rejoin the world. Either in co-existance with the Ape and his titans, or turning titans back into people, mankind begins to start anew.
This last part with the wall coming down is like the last song "Outside the wall". With the intro "All alone, or in twos, the ones who really love you. Walk up and down outside the wall". I felt like matching the "all alone" with Annie, who acted solo in titan form.. and the "in twos" to mean Reiner and Berthold, that always acted as a duo in titan form. As the "ones who really love you" would hint that their massacre, while handled poorly, may have been an attempt to find the coordinate and bring peace. And the last part that links up the last and first song "isn't this where.. we came in?" alongside Eren's memory at the first chapter and Mikasa's hair length.. either that this a cycle that has continued, or that he had a premonition, or it was a "past" Eren's memory (Think Big O).
Sorry for the "Wall" of text (pun intended), but I had a lot of intertwining theories. Mark my words: The Wall will fall.