Finally I´m done with this piece. While making it I learned a lot about modelling, baking and PBR. Comments and critics about it are greatly appreciated!:)
Yep, this is a problem with the metalness workflow, and storing both diffuse and specular content in the same map. More here: http://www.marmoset.co/toolbag/learn/pbr-conversion
There was a ton of great stuff for me. Especially the PBR talks, Pixar showing their shader work on Cars3, etc. Here are the slides & papers http://bit.ly/s17shaders
If by next-gen you mean very high fidelity graphically then look into modular/tiling PBR textures and using procedural processes like Substance Designer.
the textures are done in Substance Designer, and plugged into the default Marmoset material slots. (PBR roughness/metallic + height and tessellation) the bottom graph is from Substance Designer