Comment by tptacek

I don't think this really follows. Negotiation would be problematic, but you can just version the protocols and do WireGuard v1 and WireGuard v2, with v2 in a PQ configuration. As long as the configuration about which to use is static, you're not running up against the IPSEC problem.

I don't think there's anything necessarily complicated about MLKEM that would make this too difficult.

Switching to IPSEC loses you other WireGuard benefits; the wins don't end at "just one carefully curated set of cryptography primitives", but extend into things like DoS prevention and a design that admits to processing incoming frames without dynamic allocation.