Boeing is already having to redesign due to the A350! the 787-10 is a response to the A350. Which will not be out until 2012.
The A350 is a real threat now to the 787!
The possible 60-100 US air order, possible 100 order for Emirates, Qatar plans on 80+ A350's, Sinapore has 40 on order, amoung others
The A350 is mainly competing with the 777's and the 787-9.