Well, in that case, you can have a million layers in the landscape material, as long as the shader compiles with no more than 3-4 layers for the individual landscape components. Whatever layers and textures go unused will be removed during the compilation. And with shared samplers, unless you intend specifically to make sure your product works on PS4 or non-Direct X platforms, in which case you are limited to 13 texture samplers in your landscape material, you can use up to 128 without any significant reduction in performance. Your biggest bottleneck with landscape will always be the shader complexity first and foremost. This is the shader cost to render each pixel to the screen. Since landscape and the sky takes up the most pixels of any shader in an open world environment, if either of those two things are too expensive, they will definitely eat away at your overall performance the most.