When does the first 787 arrive? Therein lies the answer to your question if you are being interviewed for a start date in the next couple of months.
I probably wouldn't ask that question at your interview as it betrays a lack of even the most superficial knowledge of your potential employer's future plans.
You're right. It has been asked many times. Sorry for being grumpy but a quick look at a calendar and a little preparation would eliminate the need for it to have been asked repeatedly.