I really want to believe they'll release vanilla realms or TBC or even Wrath, but I just can't see it. WoW's subscribers have been steadily declining for so long, I just can't see what it would take for them to actually release legacy servs at this point. I'd probably expect them to release another MMORPG before legacy servers.
What killed the game for me was LFR being implemented. With LFR in it felt like no one really wanted to pug any more. I couldn't dedicate the time to a raiding guild, and honestly, I fucking loved pugging through ICC even if the max number of bosses I ever got down in a pug was 6. It was easy enough to get a taster of raids, yet difficult enough that you'd need to be with a guild to get much further.
I also think I lost a lot of interest due to the raids being very similar mechanics to previous ones. Things like the nax dance, the Sindragosa ice blocks and even the whole build up to the Lich King fight were all fairly unique. Then a lot of raid bosses became tank and spank again, the magic of building up to a fight through an entire expansion was gone, it just felt like the raids didn't have nearly as much effort in them as they did in the past.