The main limitations is to be able to sort into only 12 bins in one pass. If you want more detail or more groups then you need more passes. Ideally it would sort into a few hundred bins at once but I have not been able to come up with a geometry that works well. The most radical idea would be a tower of 2 meters high or so with bins spaced around it like flower petals, the air jet would have to be timed super precisely to aim the part into the right bin, especially near the bottom where the velocity would be quite high.
Pick a part is easier, the software is trivial but the hardware is anything but, an 'automated warehouse' for Lego parts would be a pretty tricky thing from a mechanical point of view.
And once you're on that train of thought, the obvious end-game is a machine that re-assembles the sets, then we can declare Lego a 'solved problem'.
Now you need sub-sorters :-) I always kept my technic stuff sorted by various parts (large gears, medium gears, small gears, motors, axles, wheels, etc)
Another interesting project would be a 'pick a part' machine that used an arm and image recognition to select parts from bins and assemble a 'kit' (all the parts needed to make a particular thing)