Yeah I’m an industrial designer so metals and their use in fabrication is one of my fortes. I do a lot of programming for 5 Axis CNC mills in Radan and SolidCam too. You’re right Aluminium can often be a more expensive material depending on the market.The cost mainly comes in the form for retooling and development, it’s a harder material work with too. I think aluminum as raw material is actually more expensive and high quality plastics are even more expensive but much easier to form. Also the face id tech surely adds to the cost. I am pretty sure the the notch is here to stay on iPhone. You might be right about the oled but I am skeptical wether Apple paid above and beyond for it given that lcd can be made into pretty much similar shape.
I am probably in the minority but the screen to me is actually a mixed experience, it looks great in sunlight but the blue shift is not ideal. Plus the sub-pixel rendering lines/matrix is quite noticeable sometimes. More-so than Samsung phones due to lower pixel density.
If the notch is here to stay I guess I can avoid it until 2020 realistically. I’m not planning on spending £1k on my next upgrade so it’s possible. I’ve never been fussed on OLED to be honest so that was never going to be a major draw for me.