Thankfully (for us) on-prem customers are able to implement HTTP/2 with very little hassle. In our case it was simply a case of enabling it at the CDN (Akamai) since our site was already on HTTPS (a pre-requisite of enabling HTTP/2).
QUIC sounds interesting, but it's far from mainstream;
Internet statistics in 2018 suggest that QUIC is supported by approximately 0.8 percent of web servers
We'll be hanging on a while until we consider implementing QUIC.