An evf within a lcd. With sensor on top of lcd, once your face near to top mid of the lcd, you looking into a 3D evf.
The sony mk3 does have an evf popup, still take up some space. A7 series, been mirrorless, also need a hump on top.
So, with a 3D evf on lcd, the hump no more n no worries on lacking of a evf. This tech might be possible, nowadays so advance.
Just hoping to see such technology one day.