HTTP/3 is not a mobile centric technology. Yes there was a lot of discussion of packet pacing and it's implications for mobile in early presentations on QUIC but that's not the same as "centric", that's one application of the behavior. Improved congestion control, reduced control plane cost and removal of head of line blocking behaviors have significant value in data center networks as well. How often do you work with services where they have absolutely atrocious tail latencies and wide gaps between median and mean latencies? how often is that a side effect of http/tcp semantics?

IPv6 is the same deal, I sort of understand where the confusion comes from around QUIC because so much was discussed about mobile early on, and it just got parroted heavily in the rumor mill, but IPv6? that long predates the mobile explosion, and again, it helps as an application, but ascribing it as the only application because of it's applicability somewhere else doesn't hold up to basic scrutiny. The largest data centers these days are pushing up against a whole v4 IP class (I know, classes are dead, sorta) in hardware addressable compute units - a trend that is not slowing.

We did this with quic data center side: https://tailscale.com/blog/living-in-the-future#the-c10k-pro... and while it might be slightly crazy in and of itself, it's far more practical with multiplexing than with a million excessively sized buffers competing over pools and so on.

There is absolutely value to quic and ipv6 in the data center, perhaps it's not so useful for traditionally shaped and sized LAMP stacks, but you can absolutely make great use of these at scale and in modern architectures, and they open a lot of doors/relax constraints in the design space. This also doesn't mean everyone needs to reach for them, but I don't think they should be discarded or ascribed limited purpose so blithely.