According to Visual Novels:
Ryukishi07 from Higurashi fame is in the staff which also includes Tanaka Romeo(Cross Channel, Family Project, Yume Miru Kusuri),
a VN which would include both Ryukishi07 and Tanaka would be far too awesome for words so yes it’s probably an April fool.
However Key had/have a banner on their site about a new project since a few weeks, and as Key will have anniversary soon there could be still a bit of truth behind this.
I really hope 鍵っ子ブログ is right that this isn’t an April Fool’s Joke because this would be a sad waste of art. I guess I will have to wait until April 2 to find out.