Principled Shader is a fresh addition. Pascal worked on it during years but it was just added in 2.79.
It followed Cycles evolution and will continue. Current work done tries to make it compatible with Eevee.
But it is a little too early to have strong opinions on its evolution. Blender users don’t have years of practice with it.
In blender internal, we have a material with all settings available. When Cycles arrived with only few shader nodes, people appreciated that simplicity.
Then, they started to complain about the need to build a nodetree , energy conservation and began to ask for an ubershader to mostly only receive textures.
Except lighting guys, few people would like to return to a complex node full of options.
Principled shader will evolve. But I am not sure that respect of energy conservation will stay at its level.
We can imagine an evolution of shader nodes in general, too. (different Add/Mix Shader, specific shaders with more options and new shaders)
Actually, 2.8 is on progress and work is done to think about Cycles interaction with new layer system and options that could be added as object properties rather than at passes or materials, shaders level.