Personally, if anyone were to dethrone Asuka I feel as it should either be Ember Moon/Nikki Cross. I'm leaning towards Ember, though.
The reasoning(s) behind the wrestlers above is pretty simple. They're the only women that I can see having a legitimate chance at actually..beating her. I've heard rumors/speculation that Ember Moon vs Asuka will be happening at Takeover: Orlando, and I can just say now that I am not disappointed with that. If Asuka is set to lose/be dethroned soon, it should happen there. Better yet, have her turn heel..that'd be amazing.