Can fully-hydrogenated oils be mixed with unsaturated oils for use in food (margarines, etc)?
The purpose of hydrogenation is to convert liquid oils into semi-solids at room temperature.  Palm "oil" is unusual among natural vegetable oils/fats in that it is naturally fairly unsaturated and is thus a semi-solid at room temperature.  

Economics is probably the driving factor preventing significant research into the solution (pun intended) you propose with mixing saturated and unsaturated fats to get the desired consistency.  Hydrogenation techniques are cheap, well established, agency approved, etc.  Same idea with palm oil.

I hope I hit the points of your question, comment if I missed anything.