I have not viewed Thornhill's video. I only got some clue about his electric dipole gravity from some posts here. I think Wallace Thornhill has a lot to explain and has put himself in a very very difficult position.
My own opinion - an opinionated notion founded on the highly acclaimed paradigm of "thought experiments" and not the outmoded mode of empirical evidence - is that an electric dipole theory of gravity does not work. If such a simple manner could unify gravity and electromagnetism, it would have been achieved long long ago and Wal Thornhill would be way too late.
Wal's idea of the center of mass gravity causing bodies to polarized radially which in turn is the cause of gravity is wrong - rather hard to defend. It does not matter we go deeper into the quark levels to peek into the electric phenomena, an electric dipole is an electric dipole - that's it.
An electric dipole will always be influenced by external electric fields and free charges (always polarized external to Wal's dipole). Let's do a "thought experiment":
smear some electric charge on a thin aluminium foil. The external field of these free charges cause electric fields whose effect would far outweigh that of the gravity dipole fields - this would mean the weight of the foil would change considerably.
It is very nice if the cause of gravity is electric in nature as physics would then be much simplified. Most of us would not believe an electric dipole gravity theory works unless it is already a full-fledged theory which unify gravity and electromagnetism - unequivocally.