It's not hard to come up with a pretty sound theory on why this hasn't been developed yet. Maybe it is partially because it requires a large amount of work, but I'm sure there are other underlying factors. Why do you think it's so difficult to exchange gralats on iClassic? Recently, in-house farms sort of allow you to do it, but on PC Graal you could simply S+A and drop gralats. If anything, it's a functionality they had to work to disable on iClassic.

It's a little bit like a video game trade-in shop. Major retailers and game studios don't want these third-party options to exist. Why? Because they don't profit in any way off of games being traded between people.

When you see a new hat or a certain item on Graal that costs money, you can pay for it by gralats that you've either farmed or won in events or that you've paid for a purchased with real money. Graal is a business and they want your real money.

Every time a hat is released, Graal definitely makes money on that day. That's good for a business. If you introduce a trading system, players will no longer be encouraged to spend money on gralats. Gralats won't even be the only currency. When you can trade hats for other hats, you basically no longer have to rely on gralats. You can just trade, and trade, and trade, and Graal is slowly going to become less dependant on gralats and the game is going to make less money.

Simply put, it's probably not the best business decision for Graal to implement a (free) trading system. How else is the game supposed to make money? That's what I'd imagine has been holding it back for so long. I wouldn't be surprised if it isn't true though, taking into consideration the poor management and business decisions the Graal management have made in the past. I've never even known of a successful Graal ad campaign, etc. Who knows, I guess.