It will be used (actually the existing textures in OT are Kelvin's work), but exactly how depends on the evolution of terrain texturing system. Currently the colors are determined by biomes & color map, and ground textures are now encoded as differential YUV textures, as you can see for yourself in textures/terrain/ground/##y.dds files. That's because they have to work in procedural colorizer that combines land colors with detail textures. Therefore Kelvin's textures no longer work directly and have to be preprocessed using a special filter.
Once the underlying system is stable, it will be possible to use custom texture sets and have modifications local.