There's no way Stadia will succeed. Sure, Google care now, but they are gonna drop this like a hot potato once the promotions come through.
From speaking to devs who engage with Google on Stadia, it appears to be a tire fire, in that the Google people don't appear to care about how much work the gamedevs need to put in to keep up with their API changes (much like lots of Google services, actually).
Because of the poor devrel, I will be incredibly shocked if Stadia survives another two years.
Without a financial incentive, I'm not sure Stadia would have any games, and financial incentives don't fix the extra work needed when google change things for no reason (or not for a reason that gamedevs are likely to accept).