Sloane Stephens, Vika Azarenka, and Sam Stosur (in form Stosur somewhere other than Australia).
I think all 3 of these have shot and possibly Li Na.
Sloane is a better athlete right now as in faster and I think may be better than Serena off the ground. If Sloane serves well enough to hold her serve, she has what it takes to win.
Vika has same profile as Sloane as she is also quicker and a better mover. If Vika can hold, she wins or if you can get 2 breaks per set.
Sam when serving well can hold and if she holds, she gets confident. She would have to play at her peak like her USO win.
Serena's serve is what seperates her from the pack. Most of the other top 10 struggle to hold. But, I think several have as good or better ground game.
I hope Vika works to improve her serve and net game as this is where Serena has the edge.
Same with Sloane, she need to improve her serve and net game. She should play some doubles to improve all court game. It will pay off in singles.