I think what it all boils down to, though, is the game engine. While Bioware has modified it they still did not write it. If it's like most game engines, the code to take advantage of the 64 bit or multicore processor architecture is very deep within the engine source. I suspect that the Bioware code monkeys would not have an easy time modifying it further in that respect.
Sure they could compile the engine in 64-bit mode, but without the code to take advantage of the higher memory allocation or longer integer values it wouldn't do much of anything.
It would probably be easier for them to use a wholly different engine (or the modern version of Hero Engine) than it would be to try to modify this one and risk breaking it further.