Does seem like a very interesting addition to the cast, yeah. I don't think there'd be too many issues of overlap with Mikako, either, since they're more foils than the same archetype. That said, her situation also has a ton of parallels with Suzuka, though, to the point that I feel like it's a bit too one-to-one. Both had some upheavals in the family that resulted in them moving away for a time, underwent a drastic personality shift in the intervening years while they were separated from the group, then ended up striking a deal with an aunt/uncle to work part time at a restaurant in exchange for being allowed to stay while attending high school, with their own apartments and living arrangements covered as part of said deal. While their actual characterizations really couldn't be more different, the backstory and living situation overlap does feel like it's a little too much.