Hello njbrown great tool
Here my node Suggestions:
By order:
1. Tile sampler enhacement:
Increasy a property and this increase node input images available.
This allows complex shapes for realistic and abstract textures creation.
2. Quad transform:
It is like Transform 2D but this control 4 Points each one with a x, y property.
This allow even more complex shapes with fast workflow.
3. To gray scale:
Color to grayscale and property for random grayscale.
This realese new possibilities, and combine with import images is killer.
4. Height Blend:
Like Blend but this has Bottom, Top, Mask Inputs and property height offset (mainly)
5. Shape extrude.
(If possible) because looks like a complex one
Transform a 2D image in 3D (more or less).
Others:
While this is not properly needed but for future... It opens a wide range of possibilities:
Have a format file which is a material for drag and drop with tweakable options choosen in texture lab.
It is quite powerfull.
I imagine this is a difficult one.
Thanks and keep the good work.