We have in-game marriage. Some players such as myself have a spouse who is just as much into TESO as I am, and we run our characters together. We mara-bond our characters mainly for the XP bonus of questing together as a married couple who also grouped up with one another. We're also both premium account holders.
What I and my spouse would both like to see is the ability to add one's spouse to the property deed, so that we both co-own the estates we have. That would give my spouse full rights to decorate, add items, etc around the house & property as I have.