Dave Meltzer mentioned this week that the WWE have no return date set for Becky Lynch. She is currently recovering from a concussion she sustained on the RAW before Survivor Series. I think that the WWE should hold off on bringing Becky back immediately and wait until the Royal Rumble.
Recent rumors suggest that the plan for Wrestlemania is Ronda Rousey vs Becky Lynch. The question is how will WWE setup that match. If Becky holds onto the Smackdown Women's Championship until Mania it may be a Title Unification match. If the WWE don't want to unify the Women's titles then they need to take a title off Ronda or Becky. That would damage the momentum of whoever has to drop the title.
The WWE should have Becky vacate the Smackdown Women's Championship due to injury. That would take care of the title problem without having Becky lose a match. A tournament could be held to crown a new champion. I don't think this would have a negative effect of Becky's character. She is capable of keeping her popularity going through Twiiter.
That will lead to the Women's Royal Rumble match. Could you imagine if during the match, Nia Jax is clearing the ring; tossing people over the ropes left, right and center and the crowd are booing her out of the building. Then, the countdown finishes and Becky's music hits. That building would erupt! She would be the most over wrestler on the planet, male or female. She would go on to win the Rumble and challenge Ronda at Wrestlemania.
Ronda vs Becky should be the main event of Wrestlemania. Ronda Rousey would attract mainstream attention and WWE could continue their "Evolution". This will be the most anticipated Women's wrestling match in WWE history. It makes so much sense to have this main event. They could play it safe and have Brock Lesnar main event against Seth Rollins but unless a huge feud comes out of left field, I can't see another match having this much hype surrounding it.