I keep thinking of that old piece of promotional art from the Warcraft Alpha that shows a Night Elf player with a blindfold and wielding warglaives. I had always prayed we would get playable Demon Hunters when TBC was announced, but they never materialized. I know they were planned to be playable long before Legion, but they devs could never make them work before then.
It would be really cool to see a TBC era version of the class, and I wonder how hard it would be for them to implement it.