@LukasPJ was trying to improve the blending between the layers by factoring in normal maps. This is different from what @ saindd is describing. In @ saindd version as you raise and lower terrain the texture will change as it's height based, not painted on.
For instance it often goes sand at the lowest, then grass, rock, snow. That way you can just sculpt your terrain and the texture comes naturally.
Actually, going off the linked video, it is indeed talking about material blending via height/normal info, to get more natural blends.
Also, T3D does actually have an autopaint function for terrain, where you can select a material for autopainting, and then assign a min/max height range, min/max slope angle, and coverage percentage. It could be better, but the root functionality is there.
@ saindd As Duion said, Lukas started work on it, and got pretty far, but there were some roadblock issues that prevented it from working alongside everything else, so it hasn't been integrated yet. It would indeed be excellent to get back to it to get it working and into stock. The thing of it being that with the way the terrain materials are set up, it allows you a TON of materials to be painted on a single terrain, but that comes with limitations of channels and blending methods.
It should indeed be improved, but it's not as easy as just slapping the blend function into the existing terrain shader and calling it a day.