Google already has the biggest gaming platform in the world: Android, and it's biggest store: Google Play. And Google Ads, one of the top ads platform. And the data from YouTube, Gmail and Google search where they extract super useful data to know who and where place their ads accordingly with the best targeting possible. They also don't care of having "free" services a ton of satellites for Google Earth or a gazillion servers as Google, Youtube or Gmail should use for that massive scale. So for the server technology they also are top.
It's impossible to be in a better position than Google to address gaming. They won't need marketing outside their environment. And knowing that most Google services are "free" for the users (users pay with their user data, not with their money), I see very likely that they may have exactly like the same than PSNow or Nvidia, even if with worse performance, but without asking players to pay a subscription in exchange for their data and putting some ads in its store.
Google would have a massive success in terms of market share getting there a gazillion users destroying their competition and creating a game streaming monopoly as they did in other markets with their main products. They would get money from the ads placed there (a tiny portion of that money would get to devs), for using this user data to improve their Google ads targeting on top of asking devs for the 30% of the IAP/DLCs from the games introduced there, in addition.
I think it's the more likely scenario, and there is a very worrying thing here: how devs are going to be paid for putting their games there. Maybe as Facebook did with games and later Google did with youtubers, during the early years they may help providing a ton of virality and good money conditions only to grow the platform and then years later to reduce and reduce this visibility just to force devs to pay them for ads, that would raise in price over time.
As always, this only would benefit the top games/publishers/devs and for sure would hurt small devs/indies. I think that anything related to pay devs a fraction of the money raised from a subscription or ads is going to be bad for devs as already happens in the other F2P (mobile)/subscription/game streaming platforms, Netflix or Spotify unless people accepts this platform as something to place there your old games that after some sales seasons and price cuts doesn't generate more revenue so you put it there to get at least something from catalog games.
If Google wants to do something healthy for the industry they need to offer this platform for free to the users and to sell games as they are sold in console or Steam: $60 new AAA games, $20 new indies with some sales seasons and price cuts for older games and ask devs a 30% or less of that. And help devs using all that user data that Google has from different platforms to know what exactly which games are going to like each player in a way that they can customize their featured games, recommendations section and ads of their store to each user. This would help everyone to get visibility, even the small devs who target tiny niches. If a player likes bullet 2D hell games, then show him the bullet hell games he doesn't already have there or in other platorms. If he prefers AAA shooters, then show him them. If he likes visual novels instead then show him these ones. These would be awesome and would create more niches and to make many existing ones more profitable, or could even help to revive forgotten ones.