SCTP: The FORWARD-TSN chunk was introduced to support selective unreliability: it allows the sender to tell the receiver that it will not retransmit some number of chunks, and requests that the receiver consider all these chunks as received.
QUIC has a much better alternative to FORWARD-TSN, either via RESET_STREAM or QUIC datagrams.
I've implemented SCTP before to hack in "datagram" support by spamming FORWARD-TSN. Fun fact: you can't use FORWARD-TSN if there's still reliable data outstanding. TSN is sequential after all, you have to drop all or nothing.
QUIC as a protocol is significantly better than SCTP. I really recommend the RFC
