I seriously don't see the "free" 1080p streaming staying free. Not once Google sees that of the few that do use Stadia are going to just stick with the free model. Once they realize how much streaming is actually going to cost them, they'll put a price on it. It may only be $5, but any cost is going to turn off some. I also can see them jacking up the 4K price to $15. Google is not going into this business to take any losses or just make a small profit.
And there are plenty of gamers who will be turned off by having absolutely no access to your games if the internet goes down. Even with digital buyers, at least they know the game is there on their HDD and they can still play it without internet. People who actually buy Stadia games are going to get real pissed if there is a sudden loss of internet, either on their end or server side, and it drops them out of a game.
The fact that online multiplayer has been put behind a paywall on consoles must make people believe that there are significant costs involved, but there aren't. Besides, the costs for an online component are already covered by the price of any given game, so the paywall's purpose on consoles is to make gamers pay for the same thing twice, all under the disguise that they are getting good value for their money.
Google is more than willing to take losses. Their Youtube platform has been a money sink for many years, but they've been okay with it because of the synergy with their core business; that is, collecting huge amounts of data of users to provide them with ads of products they may like which in turn brings in lots of money from ads.