[baybal2]

Yes, the biggest thing about Quic deployment is that UDP other than most well known ports is being firewalled almost universally on low end ISPs.

In the end, a QUIC probe, and a subsequent TCP fallback would be worse than well done TCP, and no better than MPTCP/TFO/SCTP/DCCP (all of which were supported by mainline OSes for a long time)

[amaranth]

I believe macOS/iOS is the only major OS with MPTCP right now. Some others have patches available or are in the process of landing their own implementations but that'll likely take a bit and still doesn't include Windows. SCTP is supported by most kernels but usually can't get out of your local network before something either explicitly blocks it or can't understand it and so drops it. DCCP won't even work on your network, unless your network is only Linux machines. TFO is blocked by enough junk middleboxes that, on average, it's less efficient than just not trying to use it.

Your only real choices are TCP without any extensions created in the past 20 years or UDP. Some firewalls will block UDP but at least it'll survive the open internet so that's a problem you can get IT to fix.