Not really the same thing. With Steam Streaming, you stream your games from your own PC. With GForce Now, you stream games from NVidia servers, which is the same as what you do with Stadia. Activision and Bethesda want you to double dip their games to stream from Nvidia servers.
How exactly would this work? Geforce now is not a platform like stadia despite being a cloud gaming streaming service.
They don't have a store, they just use your already owned accounts and games.