Paladins as we all know come from different faith's, - so what distinguishes a paladin from a priest must be the precepts of the Paladin Order.
- Act honourably
- Uphold what is righteous
- Fight against injustice
they do so as warriors of the light. All priest faiths can tap into the light , although some have other powers like void /death (shadow orders), nature (Loa), or arcane (Elune).
Night elves as Paladins are quite possible.. but they can do so in two ways. As Knights of the Silver Hand Paladin order use of light through Elune - Delas Moonfang is the example as she focused and was drawn most to the Light as a Priestess of Elune (whiles other priestesses of Elune can be and usually are typically more martial orientated or arcane offensive orientated). When she becomes a Paladin, one of her abilities is Seal of Elune. She doesn't lose her faith. And her light affinitiy marks her Holy.
Another incarnation is interpreting paladins as faith warriors - people who fight in battle with faith and using magical abilities.. it's like Battle Mage version of the priest. The night Warrior is a perfect example of this and would qualify as a night elven race based version of the Paladin. This is what the Zandalari paladin is effectively, but as a Loa faith warrior.
Should night elves ever get paladins, it is acceptable for them to have a choice of being a Night warrior skin of the Paladin class or just the plain