Everybody in this thread will have a Stadia account in 12 months. It doesn't need you to make a big investment. Judging the success of the service makes no sense now when it's basically in beta. When the service only costs the price of a game, then all it takes is one to get you into the ecosystem. You're already halfway in if you have a Gmail account. If the benefits of instant, platform agnostic access to AAA games isn't enough of a benefit, then eventually some exclusive will hit that pulls you in. If you don't like it, it didn't cost you more than the price of a game.
I don't think it's sunk in yet that Stadia really works. You can play AAA games on any low-powered laptop with kb/m or gamepad forgetting that it's being rendered remotely. Even if you prefer PS5 or PC or whatever, you will eventually spend some time with Stadia, and this is just year 1.