Still, considering that Red Eagle sounds very protective of their IP (and I can understand that) and considering that I really doubt the other unannounced project is a half-project even only manpower-wise, it seems a logical conclusion.
Mind you, Obsidian not doing any writing on it it's just extreme speculation on my part, and even then, they'll probably end up doing the 'small writing', meaning, they won't write, story, background and important characters but they'll still end up writing quest designs, dialogue, etc..