If we sold them roughly around the same time then yes, the Japanese consumer would be more upset but we're not selling them at exactly the same time. Also a major price difference can be because how the economy and prices of things can differ in other countries. I don't know how exactly economy works but surely you can find things that are cheaper in America and expensive in Japan and things that are cheaper in Japan and more expensive in America.
6months - 1 year can be considered a enough time for something to fade out ( this is kinda subjective).
They don't necessarily have to 'halt' the project. It can just be a side project they're working on, but not their main focus. (Lets be honest, they're doing a lot of nukige, which isn't their fault, but i doubt theres much to translate in a nukige. And most of the time people that are playing nukige probably care about 100% perfect grammar and translations. Some might but a majority probably doesnt care. Yes i know this is kind of off topic.) If they are fairly finished with the game when the final version of D.C III is out and release it (lets be nice and say)roughly 1 - 2 years later, The hype for the game won't be completely gone and people will still remember it. If they wait until the final version is out, by the time they finish people might not want to play the game anymore. People change, their taste change, and 4+ years is a long time.