This visual could as well be just a new key visual for a non-game related project for the Armored Core franchise, or just a new PR key visual for FromSoftware as a whole.
Update: FromSoftware denied the key visual is related to a new Armored Core Game.
Yasunori Ogura, who holds the position of FromSoftware’s Marketing Department Manager, changed his Twitter banner on December 4, replacing it with a new visual seemingly linked to the Armored Core series.
FromSoftware might have published a teaser for a new Armored Core game.