There's a certain bit of painful irony fans of Blizzard Entertainment see when they look back on StarCraft: Ghost. When the reskinned mobile game masquerading as Diablo: Immortal was revealed to the world at Blizzcon 2018, fans couldn't help but remember the cancellation of Ghost.
Announced back in 2002 and diverging from the series Real-time Strategy roots, StarCraft: Ghost was to be a third-person stealth game for consoles; the Xbox, PlayStation 2, and GameCube. The change to a third-person perspective was, on Blizzard's own words, “meant to to players a more personal view of the StarCraft universe”, something they weren't capable of doing with an RTS format.
Story wise, the game was set to center on a female character by the name of Nova Terra, a Terran psychic who was a “ghost” operative—and would cover a military conspiracy project being conducted by Nova's superiors.
Beyond that little synopsis, very little—if any—of Ghost's story has ever been revealed. In 2006, a novel tie-in, entitled StarCraft Ghost: Nova, was released and gave backstory to the titular Nova.
For the majority of Ghost's life, little was released about it and not much was said about it. This was unsurprising to many as Ghost was in development during the early years of Blizzard's god-like baby; World of Warcraft. In spite of that, Blizzard never officially stated that Ghost was cancelled until 2014, something many had suspected by then as the game had been dormant for nearly a decade.
The reason for its cancelation has never been outright stated, though Mike Morhaime has been quoted as saying the game was “stubborn”. It's believed by some that the reason was the upcoming next-gen consoles, and that Blizzard didn't want to release the game for older, less powerful systems. Others simply believe that Ghost wasn't working as they envisioned it, and quietly killed off the project in favor of something else—likely focusing all developmental efforts on StarCraft II.
Even before its cancelation, StarCraft: Ghost attained a meme-like status among Blizzard's fanbase, much in the same vein as Diablo III. However, whereas the latter was eventually released to the public, Ghost lived up to its title. With the ever increasing criticism towards Blizzard's games from their fans over the years, Ghost has become a recurring talking point when it comes to what Blizzard didn't see as “good enough”, compared to what's been put out by them nowadays.
In spite of that however, the main character to Ghost, Nova Terra, wasn't completely written out of the series. She appears in a story mission to StarCraft II, where he player can ally themselves with her forces or fight against them. She also appears as a playable character in Blizzard's MOBA game, Heroes of the Storm.
StarCraft: Ghost is likely to never see anything beyond the trailers that were released. While elements of it live on in other games, the odds of it ever seeing any sort of light aren't likely. Given Blizzard's notorious reputation for being secretive, it's likely all reference to Ghost has been scrubbed clean in house.
One has to wonder though what unmade projects exist of the Diablo franchise.