You are posing a very valid question which concerns both Airbus and Boeing.Technology transfer is and will be even more part of all the contracts with upcoming countries and some which lag behind in terms of a particular technology .
Just a few examples : the high speed train technology transfer to South Corea allows the RSC to bid on international markets with their own product...Japan which has gone from some time on designing local airplanes so far without any exports but they will be learning...India is coming along with technology both from western Europe and Russia...China, which has now become the leading exporter of computer components...
In my opinion, one has to make a difference between a/ design and b/ manufacture and go even further between a/ assembling techiques and b/ advanced manufacturing process.
The A-320 technology is now more than 20 years old and that's what the chinese will get with an assembly line. They won't have access to the latest wing technology nor the advanced manufacturing processes (advanced airfoil computer designs, composites, bonding techniques...etc...)
In all the examples I cited above, the top end of a product, i.e. R&D has been retained by the most advanced industrial states (Microsoft is making 15 times more money on each software CD
than Taiwan...through copyrights, mainly ).
As a matter of opinion, Boeing is running more risks with the 787 than Airbus with this contract. The reason is that Boeing has, for cost reduction purposes, given the design of major structures to foreign countries (for composite structures, to Italy and Japan).Though immediately profitable, in the long term the economics do not seem too sound as these parts will appear on the US balance of trade as imports, and that without counting the loss of technical R&D in the US, nor the manufacturing jobs lost.
It has been estimated that the chinese market for single aisle airliners will be in excess of 1500 in the next 20 years and I understand that the China assembly line will cover that need. Please also note that the contract is for [b]assembling[/] not for complete manufacturing, the way car makers are doing with low wages countries.
Finally, as BAe is one of Airbus major shareholders, I really do not think they would run the risk of a major industrial dispute on the delocalisation of the Broughton plant.
My opinion is that they are already thinking of the next technology generation they could sell after 30 years to China, after they've made a lot of profit.