If the screen is behind something like Gorilla Glass [1] like all the other tablets on the market, then that plastic will never scratch the screen. This is due to the way scratching and physics work. [2] A good reference is Mohs scale of mineral hardness [3]. Generally speaking, a softer material will not scratch a harder material. Plastics are really soft, glass and toughened glass are strong. There's a pretty good demonstration video on youtube. [4]
Interesting that you would call a plastic screen tablet well engineered. I imagine the dock is going to be the least of anyone's worries when they use this as an actual mobile device. Everything will scratch the plastic.
The screen and digitizer are not fused, which means if you can handle the bezel adhesive (and get the replacement part), screen replacement isn't an issue. Compare against.. pretty much every other tablet.