I don't know why this can't just be a cleverly laid out arrangement of layered sieves, each one parsing a different object .. I don't see how it needs to be mechanical in any sense other than "pour in the lego junk, out it comes neatly sorted", a la coin-sorting machines ..
I could see people wanting to add on color detection for the bricks, but even that could still be solved by camera + servos/steppers and a chute that goes to different bins. No need for an arm.
It is probably possible to do it, but the sieves would be quite big, just to account for the very large number of pieces, as well as having to “orientate” them correctly using only gravity.
