In terms of the name origins... I originally thought that the names were based on spacial dimensions, and then the third version would be Pokemon Z due to the 3-dimensional nature of the games. However, I noticed the third version of this generation will be the 23rd main series game released in Japan. This may just be a coincidence, but it greatly adds to the theory that the names are based on chromosomes (since the x and y chromosomes are the 23rd and last chromosomes in humans). The Japanese logos also look a bit like DNA strands, too.