SoD has clearly diverged from Classic/Vanilla/whatever, so best of luck with that, but for any future Classic+ that could come out in the future, I’ll define what I think it should be:
Classic+ is new Eastern Kingdoms & Kalimdor content, including items, gear, encounters, events, leveling experiences, questlines and lore. It maintains Vanilla systems and design as-is.
New content, no changes.