If Gotham is the origin story of Batman, wouldn’t it make sense for it also to be the origin story of Batgirl?
Dick Grayson’s birth was kinda sorta teased when the Flying Graysons appeared in Season 1, so Gotham clearly isn’t against teasing future members of the Bat-Family.
For comics fans, it seemed only natural that they would wind up getting hitched and having at least one kid.
Back in the beginning of the series, before it truly embraced the ridiculous and deviated from DC Comics canon in some spectacularly inventive ways, Jim Gordon and Barbara Kean were engaged.