The Foundation is hard sci-fi, not really retro.
While those illustrations are definitely retro style. I think it would be very hard to make a Foundation universe game and use those retro style illustrations.
Not to mention that if it is the Tim Cain and Leonard Boyarsky project, it wouldn't make sense using a pre-existing universe and lore. They are known for creating their own stuff and that's where they shine the brightest.
Also Obsidian was already one foot in the bankruptcy, I don't think they would have the money to buy the rights for The Foundation. Specially not when they can make their own universe and not be stuck in pre-existing lore.
I also don't think they would keep that fact as a secret. If they made a The Foundation game, I bet they would brag about it right away to build crazy hype and get the attention of Asimov's fans.