This is from NY Times trade reporter Ana Swanson:
For the U.S. trade representative, progressive politicians and trade experts are pushing candidates including Katherine Tai, the chief trade counsel at the House Ways and Means Committee; Michael Wessel, a member of the U.S.-China Economic and Security Review Commission; and Tom Perriello, a former congressman from Virginia who is now executive director of Open Society-U. S., a philanthropic group, according to people familiar with the conversations.
In a sign of the challenges facing Mr. Biden, those same voices have objected to more mainstream candidates they say could return trade policy to a previous status quo, like Fred Hochberg, the former head of the U.S. Export-Import Bank or Miriam Sapiro, a trade negotiator for the Obama administration who is now at a public relations firm.
It's still early, and it's all very speculative at this point, but I'm going to keep tracking these names as we go along.