Got it. Anyways, the most likely candidates are still Aki and Usami, like it was a the start, simply because of their role in the story. However, since the story has already gone this far and nothing has hinted at Aki, her chances are greatly diminished but she still has a higher chance than all the other girls besides Usami, simply cuz the other girls don't really have a special role. This is similar to how in other harem, no matter how many bitches want to jump on the MC's dick or who the reader's waifu is, the main girl is still pretty obvious.
Still though, if Aki isn't gonna play an important part of his relationship than I don't know why she was even needed to set off the plot like she was. If the author wanted to use her to tell another side of the story or to do something important that related to the MC's relationships than I would get it, but I haven't really seen any of that. Maybe the author just wanted to put her there in that role just for the heck of it and I suppose that's fine too.
Anyways, I seriously doubt its gonna be the new girl cuz: 1) She's entered the story way too late. 2) She starts out realistically shallow. 3) She has been "tainted." We all know how the nerds feel about number 2 and especially number 3, she will never be forgiven.