Thanks for the response and the URL. :)
Similar to HTTP2 scenario, devs will not have a lot to do with it. Most platforms will support the standard once it's out, since it is all about connection initiation and handshakes.
I found that H3 is being used by google and it's CDNs. So it YouTube. Pretty sure many gaming servers use H3 too. You can try it out yourself too. https://github.com/cloudflare/quiche
Let's see how it changes things. I am not entirely sure how it might affect the dev community though.