This is my personal speculation but…
I imagine certain Naaru, such as A’dal, are actually in the good graces of the ruling powers of the Shadowlands. Others, like Xe’ra, are probably the ones that actively attempted to conquer it, and thus would be enemies of the Shadowlands.
In short, I don’t think the Arbiter or Pantheon of Death deal in broad strokes of the brush.
With that said, I wouldn’t be surprised if A’dal did have a connection to a Naaru that presided over a Light-based Afterlife in the Shadowlands. There is definitely a BIG difference between Naaru like A’dal and Xe’ra. Will we see this Paradise of the Light afterlife? I’m not sure to be honest. Depends on if Zorvaal decides to either attack it, or provokes it’s denizens into attacking him.
I’d like to think it’s something we’ll see in a future patch. The characters in the Shadowlands all have connections to various souls there. Thrall obviously is connected to Draka, Jaina has history with Arthas, Kael’thas, and Uther, Baine will no doubt end up meeting Cairne, and that leaves Anduin. The status of Varian’s soul is in question, but Tiffin’s soul? That should be safe, and I wouldn’t be surprised if she ended up in the Paradise of the Light, considering she’s a source of inspiration for Anduin that enables him to wield the light to begin with.
So, hopefully 9.1 or 9.2 give us some new Afterlives to explore that are more strongly connected to a bulk of Alliance/Horde races. I imagine Orcs and Tauren, for example, might have similar afterlives. Humans, Dwarves, Gnomes, High/Blood Elves, Draenei, etc… would easily all fall into that Paradise of the Light too.