Maybe no one knows yet, but can I share a house with my significant other in midnight? With both accounts having full access to the house, freedom to change or add things?
Yes
Blizzard has already said that you can make them fully public to where any random person can come in, or make them selective access so guild mates or friends on your battle tag can enter.
You can probably get questions like this and even more than this one answered here
This is a direct quote from a developer interview from MMO Champion
In WoW housing, who can enter your house depends on your permission settings, which you can set for your plot and your house independently. You can allow anyone, or restrict access to just friends, guildmates, or even just yourself. These permissions can be changed at any time, so you can customize who visits for different occasions.
- Manage your settings: You can change permissions from “everyone” to “no one” to control who can enter.
- Permissions can be changed: You can make your house public for a party one day and private for a private meeting the next.
- Permissions are frequently checked: If you change the permissions, any players whose access is no longer valid will be removed.
- Access for your characters: All characters in your Warband can access and visit your houses, regardless of faction. You can even have one character from the Horde visit a house owned by an Alliance character.