QUIC was already common. It just wasn't coming in.
Ethereum's consensus spec just made QUIC the mandatory, preferred libp2p transport. Xatu's connection rows show that QUIC was already doing plenty of work, but almost entirely in one direction.
Across June 27 through July 10, the Tysm-instrumented mainnet sample recorded 6,884,989 outbound UDP/QUIC session opens, or 43.56% of outbound opens. The inbound side had 88. That is 0.0036% of 2.43 million inbound opens.