I’ve downloaded WC3R and got curious about the new model files, but whilst I can view them in the editor from the top down view, I’d like to see them in fuller detail. Where abouts are the .MDX files located once the game is downloaded? Because I can’t find them at all, or are they hidden somehow?
Where all game data is located for all modern Blizzard games. Inside the CASC file system.
Use CASCView (third party tool) to browse the local or remote storage for the CASC file system. All the HD assets (models, textures, etc) are located in the “.hd” folder inside the main data folder.
I’ll give this a shot later, if it works for me, you’re a bloody saint, Dr. 
What I wanna know is if it might be possible for modders to maybe replace the classic textures and models with the Reforged ones, essentially copy paste the Reforged stuff over the classic stuff.
Goodness knows I would do it.
Not likely as Classic uses different shaders. In theory the meshes and the diffuse will still work. One could even merge the diffuse with normal map for some surface detail. However the end result will still look dated as it uses different shaders which have deliberate errors in them by popular request.