I like the eternity band much better than Big Blue. It should have been retired when Diana died, it's clunky, dated, and a reminder of a not so happy union. The eternity band is fresh and symbolic of much happier sentiments.
It will never happen until more time has passed, but the ring would make a lovely clasp on a nice string of pearls. Plenty of them in the vault from what I understand.
It would be wonderful for Charlotte or George's future wife.
I just think it has outlived it's usefulness as an engagement ring.