Awesome: I've actually have three ideas that could be fun to do as side quest type content though one of them would affect the main story if you didn't already have that idea. My first idea is be once you can start doing quest you can also head to the far right and go back to previous areas, sort of treat them like bonus dungeons on revisit such as say going back to the seven eleven only to find a strange trap door that leads to an almost cult like worship led by the seven eleven monster you defeated that somehow revive (I don't know how maybe the power of corporate interest or something) that you gotta fight your way out of or you go to walikea to find the bandits trying to raid the place leading to you having to save the SCP dude from them and maybe even one of the bandits from the couch mimic. My second idea is to give someone, whether this is Rachel, John, or some random mutant, the power to copy other powers (maybe Rachel learns this after the contest and decides after some practice to rematch amber on more even grounds or john has a character moment where he finally sees himself as more useful with friends around him), to clone themselves (be funny to see someone be there own hype man, could even see them arguing and amber notes that's why the SCP dude wanted each him to be different from the others), or just alter a mutation to something else like making a random slime into a muscle bound hulk or turning Janet into something worse or better than her current state (I could imagine it being like a second raid on the college but this time its just some kid that's treating the whole thing like a game doing that "well that doesn't work because I have yada yada" and he's stopped by his parents or something)
I honestly doubt any of this would ever actually be picked up, outside of maybe the area revisits but even then, but it would be pretty cool to see what could happen with this type of stuff.