Are you actually planning to ever release a proper Runescape Gold sink? Imagines a great construction update adding a sink made from actual gold. Runescape Gold is essential in game.
The death rework(claim items form death) was a big one, but people complain if they die so they tend to complain if a boss is to hard and they die a lot etc. There are plenty of gold sinks out there. There is still far more gold entering the game than leaving the game. We need more gold sinks to make gp enter the game at the same speed as it leaves.
Sorry to say but this will never happen. Guys like me are too cheap to sink gold into things like construction and the horrible Invention skill. By "proper gold sink" I bet you are referring to some update or feature that will drain gold--that has yet to be circumvented for cheap.
Let's face it. The best money sink this game has is the Well of Goodwill. Players are too set on grinding away at monsters or skilling away to make a profit. Inflation is inevitable with typical MMOs like Runescape.
You would have to implement radical money sinks like those from EVE Online to make a difference. Of course, in that game scamming, corporate intrigues, and ruthless PVP are the primary methods of removing cash from the game's economy. The Runescape community is too skinflint to risk billions of gold on pvp even at the promise of dominating regions of the game's map. (We also don't like scamming or dangerous pvp in general.)
The RS community loves high risk. Look at stakers. There are sometimes stakes in the tens of billions. Stakers sometimes risk their entire banks.
And there are plenty of wealthy players out there who would happily pay 100s of millions for a faster skilling method. If that money was leaving the game instead of going to another player, it would be a big gp sink.
By gearing their future updates towards sinking gp instead of dumping more of it into the game, it would probably be possible to achieve a balance.