The only "Fallen but Repentant Highborne" race I'd be interested in are Naga.
The Satyr are boring. Fuzzy goat-people who live in huts, summon demons, and enjoy painting Night Elf shrines/marble pillars red. They have no real culture, no real architecture (that's their own), and little to go on beyond "Once they were Night Elves, and then they went bad!"
I could pound out about a dozen different concepts for a naga character, right off the top of my head:
An Ex-Highguard who got disenfranchised with his queen over the millennia spent in the sea, and deeply regrets what he did, and what he's been reduced to, goes on a journey of repentance.
A Tidehunter (no, not THE Tidehunter, A Tidehunter) has spent the last hundred years hunting crabs for his little near-coastal village. He is a bit reluctant about hunting non-oceanic game, but is also excited about the opportunity.
A Highborne socialite who has been transformed into a Naga Sorceress misses the courtly intrigue of the old Azshara court, and is intent on insinuating herself into the aristocracy of whichever faction she is now part of.
A Tide Priestess, born in the ocean, and a devout follower of Neptulon. She is furious as the queen for her recent blasphemies, and believes the [Player Faction] will be Neputlon's tool of vengeance.
A Naga Siren intends to take Azeroth's music scene by storm. She is already very popular among the Giblins, and thinks her unique, new style will let her push the Elite Tauren Chieftains out of the coveted Number One Azerothian Band slot.
A Battlemaiden wants to fight people. There's not much more to it. She's a Battlemaiden. It's what they do.
Gill, the Murloc-whisperer. Gill isn't good at a lot of things, but he is good at Murlocs. Very good at Murlocs. A bit too good at Murlocs. He is often mocked by other Naga for his wide-eyed stare, wide-set mouth, and general Innsmouth look (shared by many Naga who live in a little known village built inside the mouth of a dead whale). They suggest that, maybe, he and his aren't pure-blooded Naga, if'n you know what they're getting at. Gill don't care. Gill just wants to know if you want to buy a Murloc.
You can't really do that with Satyr - not unless you somehow add a bunch of new culture to them (despite the confirmation that Night Elves haven't let them develop anything like a unique culture, on account of killing them). There's not much to them. They are not a race with a lot of depth or breadth.
Edited by Sylassanna on 5/12/2013 7:49 PM PDT