I've wanted the same for a while. I think there are two main restrictions: - Mouse bodies are harder to make, since they generally have more complex curves com

I've wanted the same for a while. I think there are two main restrictions: - Mouse bodies are harder to make, since they generally have more complex curves compared to a flat keyboard. 3d printing helps a lot, but you don't get the same durability or quality as injection molding - Mouse sensors are strangely hard to find. The "good" sensors on a lot of the high-end mice are difficult to find as individual components. From a quick look at what custom mice exist, they'll often cannibalize an existing mouse for components rather than order things from say DigiKey, like you can for keyboard components