Hey, you can totally opt-in for the Stadia subscription without the bundle, but you'll then (From the latest news and pieces of informations that we got there) to wait for the real launch on Feb 2020 for that as it's currently a soft launch aiming for Founders orders to be able to join the platform, which already is something a little bit harder than it should have been.
@tycla Just to add, you do need a phone that can run the Stadia app, since that's the only way to activate your account and also buy games (can't buy games through web). So if you don't have any Android or iOS device, that might be an issue. Once you decided you want to get into Stadia, you might want to look at affordable phone that can run Stadia app.
Yeah it sucks! I already have chromecast ultra, so for me it doesn't make sense to get founders edition as it will come with additional chromecast. So even when I am willing to pay to buy a controller I can't play.
@Sachin it's too late to get the founder's edition anyway. You can still get the premier edition which also comes with the Chromecast ultra and maybe you could just give the extra Chromecast to a friend or family member? Or you could sell it. Or... Even better...If you know someone who got the founder's edition, get them to give you their Buddy Pass which you can activate as soon as they give it to you. Then you could play without having to buy any hardware if you don't want to.