Signing a guy who was a part of WWE's biggest act of the last few years would be exactly the kind of move AEW should make. It would signal they are for real and making moves to get the biggest name talent they can.
As far as Ronda/Becky/Charlotte, Dave's been clear that the idead for Mania was always a three way but that was before everything took off the way it did. He said that the logical move is a one on one match with Ronda/Becky since it's clearly what the crowd wants, but he hasn't heard anything to indicate the plans changed yet.
Given the company's MO of forcing what they want over what the fans are begging for, the three way seems like the probable way things will go.
Another thing he mentioned is how both Ronda and Shanya grew to hate MMA fans due to all the shit they got on social media, and while Shanya's ok with it now in wrestling since she's playing a heel, Ronda is still easily shook when a crowd turns on her like they did last night.