I haven't got an idea why the Mirrors won't be added in the finished route. Sure they won't mirror anything, but it still adds to the realism. Also from the Stream i saw the switches and the bones were finished for the Mirrors.
They should make the rearview mirrors even if they don't reflect as for example in the Allegra. On other trains like the 628 or the Allegra the mirrors work but do not reflect. It would give much more realism if they made the mirrors open and close even if they do not reflect
Modders can, apparently: https://forums.dovetailgames.com/threads/my-modding-projects.76097/#post-750643
It was meant more as a reference to DTG, if modders can do it, sure DTG could do it as well. I am also assuming that it must have something to do with performance. Probably also the reason why we have never seen these mods actually materialising and released.
Im by the way referring to mirrors like the br 628. So not mirrors that mirror anything but they'd still exist. Since the Breaker for the mirrors are controllable and on the Display when changing to german power it says that the mirror pedal can only be used below 5 km/h Almost as if that the mirrors actually are meant to be in the game but it didn't make it to the finished product. Lukas also mentioned that the Bones for the mirrors were also in developement so it's kind of sad that all that progress goed to waste.