I was on Tauri’s Evermoon server for a while (highly recommended for anyone who wants a close-to-retail PVE MoP experience) and have been dabbling in Turtle WoW lately. Eagerly awaiting Tauri’s Legion server in as many years as it takes for them to get it it ready!
I second Tauri Evermoon server, and highly doubt their Legion server will ever come out. Would love to be proved wrong though, except for the fact that it destroys disc priests.
I don't see why it wouldn't - they've been plugging away at it all these years. I'm sure it's years away yet, but considering Blizzard doesn't seem interested in making another good expansion, there might not be a desire for any more after it.
Late to the party, but I'm mostly playing on Warmane's servers. Currently switching between Icecrown for the population and quicker levelling, and Icecrown which is much harder and slower with 1x rates.
I started on WoW Hardcore for the permadeath, and Kronos for the full Vanilla experience, but they're much less populated so they don't "feel" as much like MMOs, but rather RPGs where you can talk to and join others if you organise to meet up... which is fine of course, and I enjoy them, but I'm preferring the MMO experience right now.