So the issue in my mind is that the new Fiesta is moving up-market to make more room for the Ka. I mean just look at the interior, it seems pretty well equipped and the assumption is they also improved NVH as well as interior materials. All this adds weight and while usually new models can drop some weight, this Fiesta is on the same chassis as the last so I really don't think we will see any noticeably change (more than 50 pounds) in curb weight.
Also the issue with the 3 cylinders is that all it's power will basically come from boost to hit 200hp. Meaning it will feel sluggish off boost, and from a tuning perspective, cylinder pressures within the cylinders is going to be absolutely ridiculous. Obviously tuning only affects a very small percentage of the marketplace, but that is why I'm off put by it.