Note that the previews below are merely recreations. It may or may not be accurate to what it looks like in-game. The previews will possibly be tweaked in the future to be more accurate.
The Dragon Engine shader code is currently less documented (because of personal preference) than the Old Engine ones, so there may be more inaccuracies here.
Stored in the red channel. Controls how shiny a texture is.
From values 0-0.1, it controls the specular intensity of a material. From 0.1-1, it controls the metalness.
In hair shaders, the first value in the specular JSON data acts as its "MT red channel".
Stored in the green channel. Occludes light on certain parts of the texture. Same as Old Engine.
Stored in the blue channel. Some shaders have the "[rough]" tag, indicating that they use roughness instead.
Stored in the alpha channel. Masks the _rd, _rt, and _rm.
_MT textures but for patterns. It's hard to explain what they do, but they basically "lock" the MT to a certain range. The code that combines MTs and RMs can be viewed here.
The green channel is multiplied to the _MT's green channel.
Similar to _RM textures. The red channel adds a lint-like effect to the base color. If it has a value of 0.5, then the base color will not be affected. If 0, the base color will become black, and if 1 it becomes white.
The green channel has the same function as _RM textures, but it also affects the roughness. (TODO: is this true??????????)
It is scaled with UV1, but is then scaled additionally with 2^x. (x is usually 3, should be in the 4th row, 1st column of unk12)
Subsurface scattering maps. Used for materials like skin and vegetation.