Well the Problem lies within Cycles: We would have to mirror the whole functionality with exact the same code to get the exact same behavior, which we can’t really (as this even varies from blender version to version).
It’s also not necessairly what you really want, because for a game it’s better to just look up the finished texture instead of going through all the steps of generating noise (it’s a kind of tradeoff: The Nodes are awesome because they can all be translated to shader instructions, so it saves VRAM but especially noise takes GPU Power). Actually thinking about it, it is a nice idea, especially if one wants to tweak parameters during the game, but it’s unfeasible.
So what you want to look into is “baking textures”/“exporting textures/maps”. That’s what Substance Designer (paid software) offers you and I think it should be that BSDF’s node’s input which you want to export into png files. I guess there should be blender tutorials about that