The system would allow you to stake items but they'd go for the averadge cost in the grand exchange and also be rounded down to the nearest 5mill or so (this could also help so rwt couldn't add a random number so they could select the person they want) depending on how much the stake is (so if you bet a blue phat and it is worth 456 mill it OSRS gold will be placed as"stake:455m") stakes will need to be exactly even unless you are fighting somebody within 10+ battle lvls higher than you. They then could double or tripple if necessary. The maximal bet limer per stake will be 850M so that you could not stake more than that. You'd also only be able to stake one item but it might be a noted item up as high as posible provided that it is 850M or less.
This is one of the most original ideas I've seen to reimplement dueling. I enjoy the notion of a grand exchange-like system, also it induces RWTing to be somewhat risky. However, Real World Trading would continue to be possible, and there would be several ways to circumvent the machine.
The biggest problem I see is that the staking of things. A player buying a blue phat from an illegal RWTing sight may face some trouble getting their dealer in a duel, but a Runescape 3 gold player who asks a stake of a grim phat, adamant warhammer, and crimson bead may not. This combination would be so random and improbable there could be little to no possibility of the player not obtaining the RWTer he's purchasing from within a duel.