Looks promising. Tried it on UE4, and I could see how it's going to be useful.
- UV maps weren't aligned perfectly. There are white lines on vertical edges of the block. (https://imgur.com/NagYBvN)
- Some surfaces have non-uniform edges which create undesirable pattern. (https://imgur.com/7FWwfdT)
- Textures are a bit too small for the block size. I think 256x256 (or higher) would be fine since they're going to be instanced and can be scaled down if needed.
Keep it up!