There is a switch that gets flipped but this dev has the general good practice of putting switches on every dialogue choice that isn't straight up fluff. Name of the switch is "day17_fiona_talk_more".So theories about who the Blackmailer is aside for a moment, do we know for sure yet how much the choice with Fiona at the end of the last update will actually effect yet? Or is that one still unknown? I know sometime devs will say before their next update on some games, and I wasn't sure if that was the case here, lol.
It might go unused, might be used just to change some dialogue a tad bit or be referenced in the story recap at the start of the chapters. I do not think it will be a course-changer for Fiona's content but that's also a possibility.