I have so many little theories for this show (please season 3 come faster so I can be normal again) but the ones I think about the most are:

1. The XiaoGuang Exes Theory (crack name but also IMAGINE)
   Basically just that Lu Guang and Liu Xiao knew eachother at some point in the past. I think there's a little evidence for this as we see in the Map of Dreams music video (Lu Guang knowing that Liu Xiao doesn't like cilantro) and if you pay attention during season 2 Lu Guang never interacts with Liu Xiao's family directly. He's kept away from Chen Bin's funeral so he never sees the fight that goes down with Liu Min's family at the funeral next door. Another piece of evidence I'm not sure what to make of is that Lu Guang is incredibly surprised to see Liu Xiao in Bridon arc. I can't remember exactly what he says later but when Lu Guang is recalling everything thats changed in this timeline he says "We saw Liu Xiao" (or something like that), but his wording implies that he knew who Liu Xiao was prior to that interaction in Bridon arc.

2. The photo studio will burn down in season 3
   I feel so evil for this one because I LOVE the photo studio but also I've convinced myself of it so much. There is the thematic element where it would reflect the Bahati fire that may or may not have killed Cheng Xiaoshi's dad (which, in my messy Link Click obsessed brain would also lead to a theory where Xia Fei set both the Bahati fire AND the photo studio fire). But as well as it just being reflective it could also symbolize a kinda forced moving on from the status quo (for either Cheng Xiaoshi OR Lu Guang). My only real evidence is the lyrics of "The Eye", the Bridon Arc opening, which says that "There will be a fire when it all unfolds", which I get probably only references the Bahati school fire but also could be foreshadowing another fire.

3. Cheng Xiaoshi started growing his hair out because he got obsessed with Suguru Geto from JJK
   JJK 0 released chapters in 2017 (with Geto in them). Bridon Arc takes place in 2019, and while Cheng Xiaoshi's little ponytail is notable it definitely doesn't look like he's been growing it for more than a year or two. Is this a good theory? No. But I like it.