I found out why they did not implement metal shaders in their doom3 based engine games.
I modified the pro-q3tourney4 bluemetal1b_shiny material so he acted like the bluemetal1b_chrome material (the metal which we have in q3tourney4) and run some random demo with timedemo 1 with and without that material, on full details.
The results are relevant I think. Without that material I got 119 fps, and with that metal material on the results were giving 64.9 fps, so the performance drop with almost 50%.
That's why they removed quake3 shader instructions when they made doom3, they did not want to have people doing fancy things, trying too much and looking in their engine to find out it is a bad concepted engine.
There might be a small possibility that material in particular is causing such a fps drop.
Unless they change some code, maybe remove real time shadows, I expect to see more Id games coming out with plastic aspect materials all the way.