I haven't debated Philli in a long time, so here's my take:
1) Dunno why one would throw in Li Na. True that Masha has dropped the ball a few times with China-girl, but the head2head is 8-5 Maria's favor. Li is competitive, that's all.
2) Serena would have retired or wound down like her sister by at least a year ago--if someone didn't pump her up with dope to keep her on court as a symbol of the dying Amerikan hegemony. They wanna push her all the way to Rio--and may kill her in the process. Keep watching, you'll see her crash on the court. Takes nothing away from her actual accomplishment to say she is now a mere curiosity. How can one find an authentic rivalry with that? 
3) The one to beat is Vika. You know my alternate-world scenario where Chernobyl did not melt down & Sharapova & Azarenka are the girl tennis stars of Belarus? (And like each other no better than Ana & Jelena in Serbia.) There is a point to the fiction: they DO sprout from the same pod. This is, in its own way, a sibling rivalry--and most difficult to resolve.
"That's the way the world works... right now." --Maria Sharapova at 17