That's a very hard thing to do. i would require an enormous amount of work to try even try that. If the full world gta III with cars and pedestrians is modded into gta 4 than that already would be an enormous masterpiece.
I think its realy stupid to convert a game to RAGE and leave it low-res textures and bad models, like, you convert the game to RAGE for the graphics, why not to make it 100% HD? it's not going to ruin the game if a building will be 1024 or 512 instad of 64/128 and better model, or better look cars.. I realy hoped for realy HD RAGE convertion..