Kojima Productions PR manager, Jiro Oishi, has recently posted on Kojima Productions official blog, known natively as "Koji-blog". According to Oishi-san latest post, at the very start of development, one of the concepts Kojima Productions had for the new game was to make it Metal Gear Solid 5.
There may be some MGS fans who remember a "5" appearing in the background of the pre-E3 2009 countdown, well this is exactly where it's use comes from.
Oishi-san says that although the game no longer has a number attached, he believes the quality of the game's content has become the highest level of the series numbered titles so far. High praise indeed, from the PR man...
Thanks to Koji Blog