Some things to keep in mind if they did this.

They would have to change the dat file system to add proper mipmap support (this is a system that adds smaller versions of every image to stop shimmering as you move closer / further away from things), every single file would need to be updated and mipmaps added if they added larger textures. This is something near every game has, and something they could not add to XI because PS2 hard drive space was so limited.

The PS2 and more accurately the hard drive limitations off the ps2 crippled this game.

I don't even know if the devkit has the functionality to add mipmaps, if it does it would still require every file to be manually updated. That's a lot of work.

The install size of the game would more than double.

This is purely if they did a simple remaster and added the original textures or scaled them up.

It needs to be kept in mind that modders do things in ways that would never be allowed be a proper game developer, so just cause modders can do something it doesn't follow a developer can do it the same way.