All true, and let's not forget that Material Recycling Facilities (MRFs) sort plastic from waste streams all day long. Its what they do.
Anyone who has visited a MRF or worked at one knows this. Republic, Waste Management and yes, Rock-Tenn all have many MRFs as part of their operations. Municipalities have MRFs as well... which is why anyone claiming problems with "source separation" is claiming a red herring.
1) there is plenty of optimal plastic which can be obtained without much effort; 2) they save tipping fees; 3) they save expensive landfill space (thus the environment); 4) they create usable fuel that can be used their plants and in fleets (eventually); 5) tax benefits; 6) positive publicity
All of these things will assist making processors extremely viable (especially Waste Management Companies - and there are lots of those around the world).