The most distinct gameplay feature added in the v1.1 era updates was the introduction of upgradeable hooks. Before this, players only had the basic Hook.
PrevTerm Mismatch Recovery
Clock Skew Immunity
Network Partitions + Leader Failure Edge Raft v1.1.01 Beta
If you are looking for the features introduced during this specific version bracket, they were foundational to the game we know today. The standout feature was: The most distinct gameplay feature added in the v1