What happens when Boeing runs out of numbers for their A/C designs? They went from 707 to 777. I think this is starting to worry Boeing management a little since the introduction of the 7E7. Another pickle is the 737. They're up to -900 models, what's next? Also, why did the 757/777 series begin with a -200 model? The rest of their A/C started with a -100.
Airbus on the other hand did a better job (at least in my opinion). However, are they planning to fill in the spaces between the A330/340 and the A380? One can only imagine what those planes will look like!