But I wonder... if QUIC does end up entirely supplanting TCP, that means it's an entirely different networking scheme. We'd no longer be using TCP/IP at all, but something else. QUIC/IP?
I agree with this and would add that the HN crowd is very HTTP browser and API centric. There are hundreds of thousands of applications that will be using TCP and not be updated until the internet is shut off. This is especially true for B2B applications. Just getting them to update cipher protocols is like pulling teeth, each time. There are an amazing number of "business critical" applications that are running ancient libraries, protocols, etc...
TCP and UDP will never go away but browsers and some API libraries may stop using TCP. More likely additional Layer 7 protocols may get added to TCP and UDP and people will use what works best for their application needs.
Do you know of any examples of these "walking wounded" applications? Can we bring some attention to reduce their foot print.
More useful is finding newer, supported and open source applications that can replace their functionality but that's a whole other topic around prioritization and people paralyzed by fear of change due to the amounts of money flowing through their unsupported applications.