I don't think it will convert many people from PC or Console to Stadia, but it will expand the market overall and bring in a few more casual players and people who were on the edge of buying a console but never quite did it.
I'm very interested from a technological perspective, but not interested in getting it until there's some worthwhile exclusives. Looking forward to some proper benchmarks, be interesting how much more lag there is in Chrome Browser + Mouse/KB mode compared to Controller + Chromecast Ultra mode. As I understand it that's how they made it playable, removing the stack and having the controller connect directly to the server but obviously browser mode doesn't have that advantage.
I actually think the lag is doable, for certain game types. 30fps adventure games that are already laggy (Assassins Creed for example) I bet will be impossible to tell the difference. Picture quality though, 40mbps 2160p VP9 is going to look very rough compared to direct render and will be immediately obvious.