Although Metal Gear Solid is one of the PlayStations top exclusives, creator Hideo Kojima originally wanted to end the series at Metal Gear Solid 4 with the death of Snake.
"I wanted to end it at every step along the way. In Guns of the Patriots [Snake] was supposed to die," Kojima admitted. "Everyone on the staff really wanted to keep him alive, so I caved a little."
Kojima also mentioned that the series has strayed away a bit from his original vision since the series' original game released back in 1998. To this, Kojima stated, "looking back at it now as a producer, I think as long as people want to keep on playing it, I want to keep on meeting that demand. So I don't think it's a bad thing."
"I'm a creator at heart, but at the same time I also have to manage the business aspect of it," he continued. "How do you put in enough to make sure it sells, while remaining true to your vision?"
Kojima did not reveal whether or not Metal Gear Solid 5 is definitely under development, however, he did admit that he feels like he will have to make the title at some point.
Source: Official PlayStation Magazine