RMT can likely be killed off with a few changes.

The addition of the merchant has rendered in person trading obsolete. It's a dated relic far too easy to abuse. By forcing a transition to the new asynchronous trading, converting all premium tabs, you can effectively kill off RMT and do wonders for the economy moving forward. There are little to zero downsides to this that can't be addressed with specific features added to the merchant. Other details can be hashed out over time.

Outside of RMT (but likely invovled) the currency exchange manipulation that probably exists shouldn't be a hard thing for them to track or react to in real time. Put up sanity checks for orders. Monster Hunter Rise did this with modded gear. While you could effectively run the optimal build, it wasn't impossible gear. Apply that to exchange rates by removing insane requests or flat out not allowing them. Upward and downward pressure on the value will be a lot more natural. Beyond that, GGG can see every single trade made.

The only argument I forsee against this idea is that you could easily put up a terrible item in your merchant tab for an insane price. I agree, that's a problem. That's where price checkers come in. We know and GGG should know the rough value of an item. Again, sanity checks solve this by putting in ranges. It would have some teething issues no doubt but to kill off RMT is to massively help the economy moving forward. With the economy fixed, the casual players are more likely to be retained through a league. That's your bread and butter. More players for a longer period of time.

That said, I doubt any serious attempt to crack down on RMT will be made. RMT in many games generally implicates devs/people with access to things they shouldn't. On top of that I'm more than convinced several big name streamers would be caught up in it. At the end of the day when your profit is dependent on viewers, paying to win when nobody is looking is a simple solution. RMT is a massive problem and a multi million dollar industry when you combine the games that suffer from it. The solutions never pretty nor perfect. But it is worth it to keep a community growing rather than fleeing the moment inflation hits. Which was damn fast this league.

God speed, GGG. I wish you the best of luck attempting to fix the game. This is my first go round with PoE and I rather dig this game. Cool lore, lots of theory crafting with builds, general esthetic.