Right now the terrain are self smoothed, but it can create some gaping, leaking and floating issues when the terrain blocks are closed to material blocks like wood planks.

IMO, those material blocks should not be smoothed, but the edge of terrain blocks should try to smoothly attach to the connecting vertices to fix the gaping, leaking and floating issues.

This issue hasn’t been closed because it’s a planned feature.

Smooth terrain (using Surface Nets/Marching Cubes/Marching Tetrahedra) already connects more to normal blocks (cobblestone, planks). I don’t have the expertise required to make a mesh generator that can connect to building blocks the way you’re suggesting and still look “natural”.