That's the issue with hot-shotting people to "invincible heights". Who will beat Nakamura? Who was going to beat Finn when he debuted on the main roster and ran through the entire main event scene en route to becoming Universal champion? Luckily, this is pro wrestling, and the results are pre-determined. In every combat sport there are upsets and there are unbeaten people who finally get that loss (besides Floyd Mayweather) and wrestling bookers can guarantee it much easier than a boxing promoter.
So to answer your question, literally anyone can beat Asuka. As for who will beat Asuka, that remains to be seen. Ember Moon looks like the biggest candidate but I think they just introduced a whole bunch of women to the show in August. I know my neighbor Mandy Rose is now performing on the tapings, maybe she can get herself over as a heel and be the one to de-throne Asuka. Maybe it's her friend, Daria (who is also currently a heel) who gets herself over and earns HHH's respect backstage. My point being, when the time is right, Asuka will get called up, and when that time comes she will drop the belt to next best woman in the division. Don't count out that new crop of women just because they're new (or not Indy veterans) everyone has to start somewhere.
"It's not arrogance; It's destiny."