Additional story-based content for Metal Gear Solid 5: The Phantom Pain, is not currently in the works.
This comes from a tweet by Konami's community manager for the series, Robert Allan Peeler. His response was to a fan question, as part of a longer conversation about the game.
There will be new content in the form of costumes, as shown at Tokyo Game Show last week. The publisher showed off DLC that includes new outfits for Snake, as well as his horse. There is still no release date for that.
Peeler also confirmed on Twitter that Camp Omega, a setting in The Phantom Pain's prelude, Metal Gear Solid 5: Ground Zeroes, will return in Metal Gear Online. That game is slated for an October release on the PlayStation 3, PlayStation 4, Windows PC, Xbox 360 and Xbox One. We checked out the game's playable demo on the Tokyo Game Show floor.
Metal Gear Solid 5 launched earlier this month to strong reviews, including a 9.0 from Polygon. At the same time, however, it has suffered from a game-breaking save bug since its release date. Konami has worked to patch the issue, and recently confirmed a fix for the PlayStation 4 version of the game. In the meantime, it has also offered a workaround to avoid save file corruption on other consoles.
The company was also the focus of a rumor last week that it had shut down development on all triple-A titles, save the Pro Evolution Soccer series. No confirmation of this has come from Konami, which also saw controversy earlier this year with the mysterious exit of Metal Gear creator Hideo Kojima.