As I said, I don't think it's likely or an actual cause for worry. But what this comes close to causing worrying about is if a majority of people using the web were using a non-standard protocol to browse it. That's completely antithetical to the idea of an open web.
Right now, 50% of Chrome users (the #1 browser), on Google websites (some of the #1 websites), are in that state.
This is only Google sites visited by Chrome. It's not like you can't visit these Google sites with normal HTTP with other browsers, nor does Chrome use QUIC on the rest of the web. If they walled themselves in then I could see a cause for concern but right now, even 50% of the traffic between Google sites and Chrome is still nowhere near the majority of internet traffic in any sense.
Because the web is open and massive is precisely the reason why changes like these will not happen overnight but potentially take decades. The amount of old legacy stuff on the web including protocols, implementations, security holes, ipv4, etc that seem like they'll never get upgraded is far more worrying to me.
Right now, 50% of Chrome users (the #1 browser), on Google websites (some of the #1 websites), are in that state.