Suggestions on Future 3D Printer Design

Current printers utilize circular extruders. These extruders have a fix width. If you would like fine details on your print you should use extruders with small nozzle size (I use the term nozzle size for the nozzle opening diameter). The downside of this is it takes a longer time to print the object while only small amount of plastic can be extruded at a given time. If you would like to shorten the print times and do not require detail on your print you can use extruders with larger nozzles.
One possible question comes to mind, “Is it possible to have an extruder with variable nozzle size?”.
A continues variable nozzle is complicated and therefore not feasible at the moment. However it is possible to have an extruder with two nozzle sizes. While printing, the printer can alter the nozzle size, either fine (0.25 mm) or bold (1.00 mm). For further detail on this subject you can read the paper   “Variable fused deposition modeling - concept design and tool path generation”.

Here are my suggestions on the extruder design:
The plastic extruder opening can be rectangular instead of being circular. One side of the rectangle can be controlled to adjust the size of the opening. With this method it is more feasible to achieve variable fused deposition system. Additionally it is possible to add channels on the nozzle to color the extruded  plastic. Special ink should be used to color the hot plastics outer surface. The ink should stay intact with the plastic even after it is cooled down and shouldn’t peel off or wash out with water. Most probably the ink used will make the surface of the plastic dull instead of shiny. However it is just a guess.

Another major change I propose, is on the plastic feeding system. The printer should use raw ABS or PLA as a granule. There will be two stage plastic feeder. First one will move raw plastic to the melting chamber. The second one will push the melted plastic from the chamber to the nozzle at a variable speed.  The trick is how to design the second stage. Most probably if it were easy it would have been implemented.
The main advantage of using granular plastic is that they are widely available and cheaper than the filament plastics used at current 3D printers. Additionally the quality of printers would be independent of the plastics shape. On the other hand filament plastics should be perfectly round and consistent in size in order to get high quality prints.