It's already been discussed over and over again, but we already know the initial 10 main LIs and Cosy considers Annabelle and Elizabeth to be almost essentially main LIs as well at this point as he's discussed on the discord. They've also been moved to the "Main" characters tab in the bios, so really you could almost say it's 12 Main LIs now. Cosy used to describe it as 10+3, but more recently called it 10+2+1. It's just a matter of storytelling and character positioning where they likely won't get as much content overall as earlier developed characters like Vicky or Lucy. That's pretty much it.
Charlotte (the last +1) is the only remaining outlier since she's the childhood friend who hasn't been introduced in the game yet and may stay slotted in a side character role as far as the menu goes, but I would still see her as ending up with MC anyway. Imo they're all going to end up married to MC at the end with chokers, so it doesn't matter from that perspective. It's just that some girls will have had more content than others. Of course Cosy could have a big storytelling epiphany and change everything, but I don't think that's likely.
For an actual "side" character that may truly not be part of the final wives/gfs at the end that may get a scene or two, my money is on Akari's college friend, the Fletcher groupie lol. She's the only one I expect to be in that position though. Everyone else is too relevant and, will be too relevant, and close to the MC.