It would be cool if you could marry everyone in game. Even if someone is married. What happens is that if they are married they tell their partner they don't want to be together and then they end up with you. And then it causes the partner to be angry at you haha.
A list of people I would like to marry off the top of my head are Hroki, Lisette, Vivienne Onis, Olfina Gray-Mane and Vex. Maybe Sapphire (not really I just feel sorry for her) and possibly Karliah.
I wish I could marry Muiri without that facepaint on and without having to
Spoiler work with the Dark Brotherhood and complete Mourning Never Comes.