Sequels that were announced then cancelled without warning.

[Segata]

It existed. That's a fact. It was quietly canceled. It still fits the topic. Nintendo even said a couple times in interviews the project was still in development. The easter egg is confirming as well the game was real at one point. Nintendo had the game on a document in E3 2005. Sakamoto confirmed it existed. He said if the game was to be finished they would have to start from scratch. The fact it was on a document means it was announced to exist. They may not have shown it but it was documented to exist and they never denied it's existence. Since you want to take things so literally. I never said formerly announced in the topic title. Just announced. The game being listed on a Nintendo document in E3 2005 is an announcement that a Metroid Dread game existed at that point in time.

[MrPopo]

I don't think you know what announced means. Companies work on projects all the time that never get announced and quietly cancelled; it's called R&D.

[Segata]

Phantom Dust. MS Announced a new Phantom Dust and just flat out canceled it not long after. They gave no reason.