Okay, so there will be some roleplaying elements, not just a straight-up battle...
Basically, what will this RP involve? Is it all fighting? Will there be a story? How much of the story will influence the players? What kind of shops are you planning to have? Items? Armor classes? Inventory?
Wushu still seems like a logical choice, but since you're including items and such, I may look into a d20 version of Call of Cthulhu. The system for that would be pretty much the same as the one I linked to, only using a d20 instead of a d100.
Yeah, there is a story. Basically, the first post will explain how all the participants were kidnapped and forced to participate in this game/battle royale (from here, your introduction post can illustrate the last thing you remember before being abducted, whether it's being knocked out by gas, hit in the head, etc.)
I was thinking of there being 9 participants in total, just like the game this is (very) loosely based on. However, I have no problems with their being less or more, as long as there's at least 5 people.
Throughout the RP, I will have one character explain the rules of the battle royale to the participants. This character will be the one seemingly "in charge" of this game.
In terms of story being influential, the main aspect of story interaction will be talking to the robots in the shops; these robots being the ones who will sell you weapon parts, medicine, armor, items and pretty much anything you need to survive battle. Also, that one character I mentioned previously will, occasionally, speak to the participants/players to impart further details and news to them, even while in downtime (there will be screens placed around the city).
While I haven't thought up of every single shop/facility, there will be a lot of places to customize and improve your weapons.
Also, there can certainly be a class system. For example, someone could be a mage, while another is of a Dragoon class or Knight class. It's up to the player.
Oh, and of course, during downtime the player is more than welcome to create their own backstory for their character and whatnot. Participants can converse will each other, though I'm not entirely sure how well that would work, as the goal is to kill each other off to escape.
However, since it's an RP, I think it'd be better if there was interaction with one another besides the fighting segments.