QUIC has some basic features for migrating a session to another link, but it doesn't support multipath in that sense. Multipath QUIC (MPQUIC) is a hot research area right now, and it's being standardized.
MPTCP's design was fundamentally incompatible with QUIC's UDP transport and session model.
From what I understand, neither MPTCP nor MPQUIC are designed to share multipath routing via a gateway (e.g. a bunch of devices sharing a multipath aggregation of 3 4G modems). It's all designed for a single device with multiple interfaces.
MPTCP's design was fundamentally incompatible with QUIC's UDP transport and session model.
From what I understand, neither MPTCP nor MPQUIC are designed to share multipath routing via a gateway (e.g. a bunch of devices sharing a multipath aggregation of 3 4G modems). It's all designed for a single device with multiple interfaces.