#2 Returns to bolster the SmackDown title picture
Unless Sasha Banks turns on Bayley (which will be weird because Banks is doing so well as a heel), where does the SmackDown Women's Champion go after she's put Lacey Evans away? I think it's pretty obvious that she will because as awesome as Evans is, I don't think her time is right now.
Nia Jax could always return as a babyface because she's going to get a massive pop when she makes her comeback from the injury that she's been battling. And she can use this momentum to challenge Bayley for the title thereafter. Even if Jax were to come up short against Bayley, it would be a pretty massive way to bring her back again.
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I suppose that with both Becky Lynch and Charlotte on RAW, SmackDown needs some heavy hitters like Nia Jax to add some firepower to the current women's division.