If you tend towards single-player, story-based games, like Red Dead etc., then maybe playing through it once and moving on is enough for you. Then again, maybe you'll want to come back to it in 3, 4, 5 years, and hopefully you'll be able to with Stadia, but with a disc/download you definitely should be able to.
On the other hand, if you play multiplayer, "live-service" games, as many are pushing to be these days, then you're already at the mercy of the dev/publisher to keep supporting the game so you can play it in the future. In that case, it become a question of who will give up support first, Google or the developer?
In either case, I think the Xbox Pass-style "all-you-can-eat" model is a better solution. No big, upfront cost for any single game, and you can still go back to something older, as long as it remains supported.