I thought that under the current 529 regulations you have to name a beneficiary who is an actual living person. Is that not true?
In my experience, a "successor plan" means a plan to have a successor owner of the account in the event that original account owner dies. In this context it has nothing to do with a (real live) beneficiary, unless the beneficiary is designated as the successor owner.
Edited to add:
From the NY Saves website:
What's a beneficiary?
A beneficiary is the future student, or the person you open the account for. You can open an account for a child, grandchild, friend, or even yourself. The only rule is that the beneficiary must be a U.S. citizen or resident alien with a valid Social Security number or other taxpayer identification number.