Cross Play isn't dependent of the ability for video game producer's. It's entirely based on the particular manufacture of the various devices one utilizes to play the video game. Microsofts Xbox, Sony's PS4 are not privately owned and operated companies, they both have investor's. Who demand a return on their investments. Making their devices "Cross Play" compatible with each other, wouldn't be conducive for an investor. What investor would invest in two opposing companies that are in competition to improve their bottom line thus provide higher returns such as MS and Sony are?