To my knowledge Airbus have always looked at the shrink of the A330 to replace the A310/300 albeit its was on the back burner with the "Big-Bird" A380 dominating its strategy.
I was involved in a study at uni with BAE/Airbus UK into using a 767/A330 type to launch large cruise missiles through the belly of the aircraft and was privy to engineering drawings that can prove the engineering viability of the A330 "shrink" - Airbus knows it will work, its all about tweaking the wing tips, TE devices and extending the vertical Stab (think modern day 747-SP).......Airbus felt that it was just not a priority then - however if it did go-ahead my bet would be on the Airbus if you look at the total package (ie. Cross Crew Ops, fleet commonality, inherent efficiency)
I've discussed the pros & cons of both stable of a/c with several of the pilots I work with and the main advtg of the 767-300 (and Boeing A/C in gerneral) from this particular Charters point of view is we can get it in and out of places like CFU - which they beileve the 330 wouldn't get into in its present incarnation. (BTW we've seen the A330 get into other Greek Islands like Heraklion).
My concern is that 767-SE will be a re-hash of Boeings' existing designs and that it'll sacrifice performance for efficiency:
As I'm assuming Mass Reduction will be Boeings primary target in the design re-hash and will propbably replace a significant proportion of conventional materials with composites - more than likely primary structures just like in the 777 but to a greater extent. These materials can be complicated to repair - requiring specialised equipment more akin to a plastics laboratory as opposed to a hangar. Would airlines save in Fuel but Pay Out in Maintenance investment?
I think it is good that Boeing is persuing this model, though I'm dissappointed that it's dropped the sonic cruiser. I'll bet there are some engineers in Seattle seriously hacked off!. At the end of the day its good news that Boeing is persuing this design - who knows what technologies Airbus will be able to half-inch!
World of Tweed
P.s. Food for thought?? - Airbus will shrink the A330, add a sprinkling of 'super-efficient' technology and tout it as "the perfect addition to you airbus fleet" and it'll be in service probably in/or about the same time frame. Such is the beauty of a modular design.