I can't think of a way of doing it that doesn't require root access. Only the root user is allowed to change the ownership on a file. Allowing a group to read a file implies the file is owned by the group with r-- attributes. Allowing one member of a group to write the file implies ownership.
You can give another user read/write access to a file you own with "setfacl -m user:sally:rw"
Now user sally can write to the file and make changes.
However, you will still have write access. Even if you don't have write permission, being the owner of the file, you can change that if you wanted to , or in vim, just add a '!' character after the "w" command to write to the read-only file.
While sally, and yourself are the only members of the group who can modify the file, sally cannot use the setfacl command on the file. The best she could do is make a copy of the file and use the "setfacl" command to give the next member write access. Now this receipient and sally are the only users who can modify the file.
This assumes that the file is located in a writable directory with the sticky bit set. Otherwise, a user with write access to the file can always use the ":wq!" command in vim, which deletes the old file and replaces it with a new file with the users default permissions. Using "cp" and "rm" can be used to do the same thing.
The closest that I can think of is for a file to be owned by person. For demonstrations purposes let's say it is owned by root.
# touch sample
# chown root:root sample
# setfacl group:authors:r
# setfacl user:sally:rw
# cp -p sample /tmp/
Now sally can edit the file. Members of the "authors" group can read it and not edit it. The sticky bit on the /tmp directory prevents deletion, so a member that can read it can't replace it.
However, root needs to change the file acl to allow the next user to edit it.
This doesn't fit your theoretical problem exactly. Linux does not allow transferring ownership of a file (only root can do that), and only the file's owner can change the file's acl.
However, an identical file owned by the next owner can be copied from sally's file. However the owner of the file is the next group member, and nothing can prevent him from doing this at any time if he has read access, but he can't replace the old one in a sticky directory.
A couple interesting things I found out myself. You need to use the "-p" option with the "cp" command to also copy the ACL. The "mv" command doesn't have this option.