Flying the A330 and A350 by the same crew is known as single fleet flying (SFF), the two aircraft share the same type rating. Flying the A330/A340 is mixed fleet flying (MFF) as the aircraft have different type ratings.
CX will not be the only airline doing SFF with the A350, this presentation by Finnair outlines their training footprint for SFF with the A330/A350. It is almost identical to what CX is doing.
http://halldale.com/files/halldale/a...i%20Vanska.pdf
Finnair also plans to MFF the A320/A350 in the future, at the moment however with the few aircraft in the fleet the A350 is flown as an independent fleet. Regulators in Europe, USA, Hong Kong, Singapore, Brazil, and Vietnam have given the green light for A350 SFF.
The main difference with the CX approach and other airlines is the A330 procedures and checklists had been progressively changed over the past year to align with the A350.
ACMS the middle east airline that is not allowed to be mentioned on Pprune is flying the 777/787 as a single fleet. They have however decided to revert the 787 procedures to 777 (ie going backwards) which has resulting in some interesting incompatibilities.