Here are supposed leaks (from reddit):
-Classic WoW is in a pre-alpha state, mostly all quests done. They started working on dungeons and battlegrouds.
-17 devs are working on the game, 2 former Nost-devs for assuring authenticity.
-They don't think there will be a long beta phase.
-Only changes: Improved textures and spell effects but still using the old models. Improved view distance and colorblind mode. Battle.net will have some restrictions on PVP servers.
-8 servers per region, 4 PVP, 2 PVE, 1 RP-PVP and 1 RP-PVE.
-No ingame shop at the start.
-Sub will be included in retail WoW or you pay less for Classic only.
-Launch about April/June 2019.
-There will be an annoucement and gameplay at Blizzcon.
This was leaked before the classic demo was announced.