On the Celestial Patron for the Warlock.
The warlock is an occultist, a dark witch, a seeker of forbidden lore. Their patrons are eldritch beings who come over and teach them dark arcane powers, sharing a personal relationship with the warlock. Their magics run to the black; madness, domination, curses. Just look at the warlock on Neverwinter. It actually uses those three Vices from the Book of Vile Darkness as the defining traits of the class. The modern warlock includes the themes taken from the 3e Binder class, where being hunted and opposed by clerics and holy religions was a huge theme. Their magics are necrotic, associated with undead and the lower planes. They bargain with creatures from other planes, bartering their service for scraps of magic and power.
All taken together, a Celestial Patron would be the exact opposite of what makes the warlock, well, a warlock! It would be an anti-warlock! The very nature of the Celestial patron is opposed to the idea of being a warlock.
In fact, in many ways, they are the exact opposite of the Paladin. Where each of the Oaths can be said to represent Justice, Purity, and Love/Beauty, the warlock patrons can be said to embody the Vices of Destruction, Corruption, and Domination. Two fey paths, one an Oath to protect and nurture, the other to drive to others madness. A devote Oath to slay demons, another that is embodied by infernalism and diabolism. A seeker of Justice and Vengence, and a Patron who teaches to dominate the minds and souls of others.
*deep breath*
And then, I point out that we have the Oathbreaker Paladin. If the warlock is truly the opposite of the paladin, then there should be a Celestial Patron for the very same reason we have the anti-paladin subclass. What rises must fall, but what has fallen may yet rise.
However, the Celestial Patron needs to work within the warlock class, and admit to the class strengths and themes, instead of ignoring them or trying to overwrite them into something else. I also think it needs its own Pact Form, since each of the three current patrons are really designed to work with one of the forms, and not the others. And we should also get a Vestige Patron with a Form of the Sigil for a binder warlock path. But that's all another discussion.