3. Is QUIC designed to natively support communications over multiple paths?

In the current (2019) state of the QUIC specification, the protocol supports a connection migration mechanism that enables a QUIC connection to be maintained in the event of a change to one of the participants' addresses (or port numbers) (including changes to addresses allocated by intermediate NATs). Receipt of a message for a connection in progress is an indication of connection migration. Thus, a connection migration consists in moving from one quadruplet {source address, source port, destination address, destination port} to another.

It is recommended to validate the new address using the PATH_CHALLENGE and PATH_RESPONSE frames exchanged between participants to validate a connection migration.