There are people making applications with requirements where we have to support the legacy browsers, unfortunately. That's how Enterprise goes (but even large consumer-facing apps have the same requirements too, I would be shocked if Facebook "didn't work" on IE 11 today).
In my particular case, my infrastructure team will not, and has no plans on, enabling HTTP/2 in our upstream servers. The joy of application development at scale. You can't get everything you want, unless you control it all. Things are too distributed for me to practically sell the team on HTTP/2.
Hire an expensive consultant to tell them what they need to hear. I’m sure if they pay $100k for the privilege of hearing they need HTTP/2 they’ll be more receptive to the need.
I am an expensive consultant. My advice is skip HTTP/2. Either wait for HTTP/3 to ditch TCP or start inlining resources into single HTML documents to reduce round trips.
I'm definitely looking forward to HTTP/3, but I anticipate HTTP/3 having more problems with adoption due to overzealous firewalls and UDP blocking. I expect a longer tail of "I can't use HTTP/3" clients than "I can't use HTTP/2" clients, which means it'll be longer before you can reasonably count on it for performance optimization.
In my particular case, my infrastructure team will not, and has no plans on, enabling HTTP/2 in our upstream servers. The joy of application development at scale. You can't get everything you want, unless you control it all. Things are too distributed for me to practically sell the team on HTTP/2.