Personally, I'd bring back Chelchis Kell of Stone. Despite there only being a handful of lore entries, he seems very interesting and despite lacking paracausal abilities, he would be stronger than most guardians since he made it all the way to Oryxs throne room just to be killed by Oryx himself. Also if we do see Eliksne guardians, I could definitely seem Chelchis being revived since he died on the Dreadnought and it's just drifting in our solar system, and since some of his artifacts survived all the way till guardians boarded the Dreadnought, it's possible they maybe enough remains for a ghost to revive him.