The implementation of QUIC is complicated, and the integration of a QUIC library with Envoy is also complicated. There is no sign that anyone will implement a different QUIC implementation in Envoy.

To simplify the implementation, we should consider removing the pluggability of QUIC implementations, and just use QUICHE (but with a build setting to remove it entirely if needed).

If we decide in the future to have an alternate implementation, I think it is sufficient to make it a build-time decision; supporting multiple QUIC implementations in the same binary, by filter configuration, seems unneccessary.