why not just http/quic?
using 3 seems strongly suggest that it is the next generation of http.
They knew that but pretend it is not relavent.
Because there's a decent chance that it will be the next generation of HTTP.
If it doesn't pan out they'll just move on. Remember IPv5?
>
>To address this, I'd like to suggest that -- after coordination with the HTTP WG -- we rename our the HTTP document to "HTTP/3", and using the final ALPN token "h3". Doing so clearly identifies it as another binding of HTTP semantics to the wire protocol -- just as HTTP/2 did -- so people understand its separation from QUIC.
https://mailarchive.ietf.org/arch/msg/quic/RLRs4nB1lwFCZ_7k0...
TL;DR the rename is to resolve the confusion.