Surface-related brush size and surface aligned brush

I would like to have the same as sculpting brush have — fixed size, related to object. Just because it is a pain to make precise texture, when geometry is not simple and rotation is used. No. Really. How can I correctly paint over the 3D model with totally 2D brush, locked in the screen dimension? Check 3D-coat as example? it have 3d-projection brushes.

The next thing is brush texture, that not linked with brush-size. Very useful to make homogenious texture, that looks as good as procedural.

To understand how at works, look to Sai2: systemax.jp/en/sai/devdept.html The scale of texture is independent of brush scale. So I can correct smallest part of large texture (i.e. scales) with very small brush. It works like stencil, but with size that relative to world/object, not the screen.

Even Substance Painter¸ or Mari still don`t have such brush. So it is the additional reason to be first and call more people to use and support Blender.