I don’t know if there has been any official information regarding basements, but I can think of basements in two ways.
Either letting multi-floor descend downwards below floor 0, or letting us move the entrance to other floors. Thoughts? What seems more likely?
I would think a downward staircase either through a trapdoor (which would be great, you could hide it with a rug) or via a stairwell room, but a simpler one than the spirals we have going up, something like a cupboard with stairs descending into the dark. From the current ground floor.
Of course if we get basements we need cobwebs to decorate with!
Couldnt you just move the entrance upstairs?
then as you enter you would technically go downstairs to the basement?
They are allready in the game.
That would require changing of spawn point in the house interior. Currently you can move the door, but spawn point remains on the same spot.
Really, where are they from? I might as well make my in game house match reality 
Vendor by the tower at the seaside in the Horde housing area. Undead female NPC sells gray stuff and cobwebs decor. Just get decor vendor addon or wowhead it.
Thank you I shall have a look next time I am in game.
Lot simpler to to just let us move the entrance one floor but to make sure you spawn inside correctly and not down in the “basement”.
You can already buy them from a not so secret vendor in a cellar in both housing locations. There was also mention of a vendor in the Dragon Isles but I have not gone to check it out yet so can’t confirm.
i agree about the easiest way would probably be moving the spawn point. just pin its location to the door and have the door always rotate so the same side faces in then set the spawn distance be fixed from the center point of the door. and for people who brake their spawn add a reset spawn location button which replaces the door and attached spawn point back to the default location