If you haven't seen the leaked images on Chapter 7, see them
Now, my personal theories about the images.
In the discord chat, Super explained that there is a section of Chapter 7 that involves a flashback to 2 years ago. The photos of the 8 pedestals were most likely during that flashback, and all the pair shots of the masters and their accompanying new characters are from that flashback. I'm guessing that the new characters accompanying the masters are either ex-masters, or their friends. This means that Crusher is paired up with the grey-skinned orange torso, Piercer is paired with Zhao, Baller is most likely paired with the pink-torso female, as they both had individual shots inside the throne room, and Slicer is paired with McSlash.
Why McSlash? It's because Super cropped the owner of the arm's face and body out of the picture, meaning that they are obviously someone we have seen before. The only character in BFS that we have seen that has a white arm would be McSlash. This also makes sense, considering that McSlash and Slicer are both sword oriented. If my theory about how the other 4 owners of the pedestals are ex-masters holds true, then it is also likely true that those 4 had names ending in "-er", like ball-er, or crush-er. Would that make McSlash "Slasher" or something? Either way, Super confirmed his death in Chapter 2, so there is no chance he will have a rematch in Chapter 7.
This brings to mind the obvious question of how these 4 ex-masters were removed from the current roster. McSlash was most likely corrupted, or was a turncoat, considering how King referenced him being "much more powerful", and how You was sent to kill him in Chapter 2. Another intersting case is Zhao, as Super stated that he was by far the most powerful, being able to wield 3 weapons. He also appears in the Spirit Arena during what I presume can only be present day.
As for the smug guy and the teal torso, I'm not quite sure as to who they are. However, Super said that all the fights in the arena were "unfriendly reunions", so those two were also probably previous acquaintances with Zhao and the Masters.
The close-up is most likely a close-up of "???" in battle armor. If you pay close attention to the hands and feet, they match those "???" wears in the cutscene in chapter 6.
As for the dead knights, Super confirmed that they were knights of the Redcliff, and that other factions like the Overseers, the Korblox, and the Knights of Splintered Skies were all going to be canon factions in BFS. However, they are neutral factions, with the Darkin being the only "evil" faction that the protagonists are working to thwart. This means that our top candidates for the culprit of the massacre are "???" from chapter 6, or another darkin member.
And finally, the statues are most likely soldiers that were petrified, i.e. turned to stone. This is evident through their strange positions that are unlikely to have been sculpted intentionally. Especially considering the final statue, which is most likely pointing at whatever caused it to turn to stone. I am doubtful that whatever petrified them would be a future boss, as the concept of petrification seems rather overpowered for a boss.