What new feature is introduced in NFS 4.1 on ESXi 6.5?

Storage DRS is a datastore cluster load-balancing feature introduced in vSphere 5.1 and is not specific to NFS 4.1 - it supports multiple storage protocols and is not a new NFS 4.1 capability in ESXi 6.5.

KRB5i (Kerberos with integrity checking) was already supported in NFS 4.1 on ESXi prior to version 6.5 and is not a feature newly introduced in ESXi 6.5.

IPv6 addressing support for NFS 4.1 was introduced in ESXi 6.5, allowing administrators to mount NFS 4.1 datastores over IPv6 networks for the first time. Prior to ESXi 6.5, NFS 4.1 on ESXi was limited to IPv4 addressing only, making IPv6 a genuinely new feature of that release.

AUTH_SYS is the UNIX-style authentication method used by NFS 3, not NFS 4.1 - NFS 4.1 in vSphere uses Kerberos-based authentication (KRB5, KRB5i, KRB5p), so AUTH_SYS is not a new NFS 4.1 feature.