I was thinking some more on Kael’thas as a San’layn, and had a pretty neat idea that could work for him or even whoever would lead a playable Horde San’layn faction.
If we did see Kael’thas comes back as a San’layn, he’s likely to have a huge weight on his shoulder, considering his betrayal to his people, losing Jaina, and other things. Such a road to redemption would be rather arduous and likely give him a lot to think about in his free time. So why not translate that into something with such feeling, like music?
Suppose the San’layn get stationed at Deatholme, and Kael’thas or the San’layn leader is in a necropolis floating above it. At specific times of day, they will move to an organ and start playing a mournful tune for awhile. Something akin to this:
Such a tune would echo for a decent distance from Deatholme, getting softer and softer as you get away from it. It adds to the atmosphere, makes for a bit of world-building, and really complements the theme of San’layn, in my opinion. Plus it makes leveling in the Ghostlands a lot more memorable if you occasionally hear that, find where it is coming from, and maybe stay awhile and listen.
The idea is somewhat similar to originally in Burning Crusade, where you’d give Sylvanas a quest item drop that causes her to summon some banshees to sing:
Little things like that really add to the game, making it feel more like a world and creating emotional attachment. Maybe we’ll see a “Lament of the Darkfallen” someday, which could also work.
The idea behind the organ music with no vocals is meant to you to feel the weight of the San’layn (and Kael’thas if he is around) and the sorrow that looms over them in general. Sure, the San’layn would likely stand proud and not show weakness in general, but there would be at least a sliver of lament for their situation that would reside in each of them. Music like the above I feel helps to translate it into something players can feel and imagine.
I’m sure you could work with this idea to make something really neat and memorable in the game.