From Software president, Hidetaka Miyazaki, has hinted that a new Armored Core game is still in development, despite the lack of an E3 announcement.
The studio announced that it was working on three games back in 2016, and Miyazaki confirmed that Armored Core was in development at the time.
However, at E3 2018, the developer announced its new VR title, Déraciné, new Souls-like samurai game, Sekiro: Shadows Die Twice, and a collaboration with Devolver to re-release cult Xbox mech game Metal Wolf Chaos.
Source: IGN.com From Software Boss Hints That a New Armored Core Is Still in Development