I love the discussion going on lately! Also hilarious flirt <3 Let me grab the flirt idea that’s one of my favorites, hang on…
Yes, I’m corny as hell. I can admit that. 
But anyway, first generation San’layn (can I even say that and be accurate? Who knows) are Sin’dorei. They were the blood elves that accompanied Illidan when he went after the Lich King. When Illidan failed to win that battle, the blood elves were left there to die. They were as a result turned into San’layn.
The thing is, these elves were very loyal followers of Kael’thas, which I really hope they use if they ever do expand upon San’layn lore. I mean, we’re seeing Kael in a vampire area. This is a perfect opportunity for him to see what became of some of his closest followers. I’d really love for Lana’thel’s lore to be expanded too.
I was hoping the Blood Quill would actually do that, but sadly, that never happened.
So, San’layn are undead Sin’dorei specifically, not Quel’dorei. However…there’s constant debate as to whether or not that matters. She could very well still consider herself a “High Elf” or see the “High elves” as her people. It’s a whole lot of weird mumbo jumbo. The distinction between Blood and High Elves is that Blood Elves renamed themselves Sin’dorei to honor those that fell when Silvermoon was invaded by the scourge.
Here’s a fun fact. Illidan vs. Lich King happened at the end of WC3. San’layn juuuuuust barely missed being relevant in WC3 lore because their creation happened directly after those events. Therefore, we don’t have WC3 lore nerds on our side. We were so close to making that cut, hehehe!
As for models, that’s a tough one. I think everyone’s been making some good suggestions. I really like Hypnos’s model idea for male San’layn ( https://www.reddit.com/r/wow/comments/8jmspv/concept_sanlayn_and_high_elves/ ) and as for female San’layn, there’s a lot that could work.
The weird thing is, the Blood Prince models do need some work. A lot of it, but they still look really cool. I feel like if those were polished up, they could be glorious playable. But…I’m pretty sure they’re attached to the gear and have no player animations or real faces.
So, I’m guessing they could grab a model, mod it, and all that. I guess the Venthyr stuff could work too if there was a version not decrepit as well. Problem is, right now it seems like San’layn and Venthyr are two different species, so using the model for both might feel very weird if Blizzard intends on adding both in some way. However, we don’t know their lore in full yet, so… 
Looking strictly at San’layn, they could pull a Nightborne (but correctly) and heavily modify the Thalassian elf model to be more lanky, lithe, and what have you. Sharper edges and all that, bat-like ears, fangs, black/red/amber eyes, claws… you know, the works.
A modded draenei for a female San’layn sounds interesting. I wonder how they’d go about that? They’d have to fix the legs, though, for sure.
