Landscape material system can’t work with vertex data because of lodding. Distant landscape component may have only 2triangles. Data has to live in textures. Restriction that ID can only change when associated blend weight goes to zero might work but it’s also can cause other headaches. Painting system then need to take care of this restriction. In our system there were multiple biomes and that was only sane way to blend between them. In other kind of use case there might be better ways.
Can’t find any links to that stochastic material layer blending system. I remember reading it in twitter comments. Really hard to find those. I will keep searching. It’s might sound crazy but it can be really big performance win. Instead of multiple layers cost would be just one + some spatial + temporal dithering logic.