This has cropped up several times when I discuss FDM with manufacturers, " why do we have to turn a bag cheap pellets into more expensive filament?"
The filament form was a solution to the issue of transferring the polymer to a moving head without overly increasing the mass, so the head can continue to move at speeds required for efficient building.

If you want to look at a system that processes pellets, look at the Arburg Freeformer, which is essentially their tried and tested injection moulder with a tattoo gun style nozzle to control the deposition. Not exactly cheap though.

Pellet form exists the world over for supplying every injection moulder, but you're buying in 25kg bags and usually subject to minimum orders.

Rich