So glad to find some like-minded folk who care about this! Nice post, Shane.

Thanks for calling out my research on this. Really glad you found it.

https://github.com/paulirish/lite-youtube-embed/pull/167 has my solution. Basically we only attempt the hqdefault.jpg and the sddefault.webp; no other ones. Based on my research this is (probably) the best solution that optimizes for both latency and coverage. Though, I could see switching the order of two in the future.

Pretty sure the oEmbed solutions folks are mentioning are only reasonable if you're doing this work server-side/eagerly. Obviously that changes things quite a bit.