Update the sprites, and overhaul the engine. It couldn't be that hard to improve upon AEGIS. Let's bring the sprites into the post 2004 era of gaming. Not just the character sprites can be updated but also the 3D zones they inhabit. I think a project of this magnitude is the next step in Ragnarok Onlines renewal process. These visual updates would be a great way to show off the game to a new audience, as marketing is best done visually in this world. I truly believe this will be necessary at some point if this game intends to stay in the marketplace for the next 10 years. Things need to be developed for GM teams as well, such as tools for creating events and manipulating the game in creative new ways. Perhaps some kind of sprite creation tool as well.
This is actually what I thought of when I first heard the term "RO Renewal" muttered from kRO around 3 years ago now. But it turned out to just be a pretty large content update. I think if they were serious about the longevity of RO 1 they wouldn't have re-started the development on RO 2 after it flopped the first time and put work into that instead.
The worst part is that it took about 2 years to complete Renewal, but they really didn't accomplish much. A dedicated studio could have remade a game of RO 1's complexity, from scratch, in the time it took kRO to finish Renewal.