OD-BWH From Kuwait, joined Jan 2002, 399 posts, RR: 3 Reply 1, posted (11 years 11 months 1 week 4 days 8 hours ago) and read 737 times:
There's no problem with Airbus regarding numbering: a good example for this being the A380! Actually Airbus still have A350, A360, A370, and A390 before the series ends. Boeing has 787 and 797 left only.
As far as the A320 family, I don't think there'll be any new derivatives... the available models cover most capacity ranges for short haul, single aisle airplanes.
Don't forget that there are A330-300, A330-200, and possible A330-100, or 500... etc. So don't worry about this