In order to get the most possibly focus on the core QUIC protocol and be able to ship it on time, several features that were originally planned to be part of the core protocol have been postponed and are now planned to instead get done in a subsequent QUIC version. QUIC version 2 or beyond.
The author of this document does however have a rather faulty crystal ball so we can not tell for sure exactly what features will or will not appear in version 2. We can however mention some of the features and things that explicitly have been removed from the v1 work to be "worked on later" and that then possibly might appear in a version 2.
Forward Error Correction
Forward error correction (FEC) is a method of obtaining error control in data transmission in which the transmitter sends redundant data and the receiver recognizes only the portion of the data that contains no apparent errors.
Google experimented with this in their original QUIC work but it was subsequently removed again since the experiments did not turn out well. This feature is subject for discussion for QUIC v2 but probably takes for someone to prove that it actually can be a useful addition without too much penalty.
Multipath means that the transport can by itself use multiple network paths to maximize resource usage and increase redundancy.
The SCTP proponents of the world like to mention that SCTP already features multipath and so does modern TCP.
It has been discussed to offer "unreliable" streams as an option, that would then allow QUIC to also replace UDP-style applications.
DNS over QUIC was one of the early mentioned non-HTTP protocols that just might get some attention once QUIC v1 and HTTP/3 ship. But with a new transport like this having been brought on to the world I cannot imagine that it will stop there.