As far as I'm aware, they've been in on and off talks with the WBO champion, Valonte for up to a year. They wanted to get her for Dec 15th, but looks like that hasn't worked out. Think they've had a hard time getting her out of Brazil.
Amanda Serrano would be a big fight, but it's for down the road, as she's dropping to 108 lbs to try and pick up another belt first. I haven't heard of many talks with Persoon, but she appears to be the best and most dangerous, so if Taylor can pick up the other belts first, that would be the preferred option.
Cecilia Braekhaus seems warm to the idea of a Taylor fight, she's more on board with that than a Claressa Shields fight. That can be at 140, or possibly a 142 catch-weight to allow the titles on the line. Jessica McAskill is also up there now as a WBC champ at 140, so there's always a rematch there too.