(Wearing my zcashd maintainer hat)
For those who have not been following Arborist calls, the current thinking is for NU6 to be a smaller network upgrade that only contains things that are reasonable for us to get into zcashd while focusing on its deprecation, and for ZSAs (which are definitely not reasonable to get into zcashd) to be deployed in NU7. This makes it feasible for NU6 to occur this year.
If ZSAs (or other major changes) were included in NU6 then there would be no network upgrade this year (as we expect it will take the entire year to deprecate zcashd, including implementing and deploying the necessary replacement for zcashd’s wallet and migrating everyone off it), delaying consensus changes like explicit fee fields in transactions (solving a long-standing UX issue), or potentially altering how memos are encoded in transactions (which is required for Authenticated Reply Addresses due to the size of Orchard-related proofs).