A feature that FFXI would really get a big boost from going forward and that would unlock a lot of the limitations would be mipmaps stored in the dat files instead of being made on the fly as is currently the case.
Mipmaps are smaller versions of each texture that are used as you move away from things. Square decided to not do what most games do and store these smaller versions of the textures in the game files due to ps2 hard drive limits, so instead they are made on the fly as you move around and this limits the size of textures they can currently use as well as many other things because they get hitching as your computer tries to make smaller versions of everything and store it in memory.
This would increase install size by 25% (if they added mipmaps to all old textures, and not much if they just used it with new textures) or so but it would allow developers to start using higher res textures.
Example of what mipmaps are: As you move away from the object the game loads the smaller images.
http://wiki.polycount.com/w/images/a...ia_mipmaps.jpg