You mirror fans out there:
PC games handle mirrors usually like another camera, so they tend to be extremely expensive.
Reflective surfaces like shiny metal or water can be easily made with prerendered maps, thus not reflecting moving objects in the world.
As soon as you want to reflect everything, you also need to render/calculate everything which can be seen -> expensive!
And as the CE2 seems to have problems with weapons firing always at the center of the screen... this might get difficult to implement. Has been mentioned plenty of times.