Hi,
The "Append to" privilege does not exist in Share dialog even in the old interface.
Let me explain this briefly.
The Append and Append to privileges are for entity level.
If you share a record's "Append" privilege, it can be related to other records. This will have no other impact on this entity.
If the "Append to" privilege can be shared, it means that other records can be related to this record. And that means that other records can be pegged to this entity.
So the "Append to" privilege cannot be shared in a record level.
