From a technical standpoint, you'd need a page to manage marriage requests on, a database table to track them, a page to display the information on, and some rules to govern what you're allowing. It's certainly less daunting than several other systems in BM (not counting the battle system because that massacres all other pages in levels of daunt).
For instance, if you wanted, you could steal M&F's concept of relationships, which may save some implementation time since that all already works, then adapt it to how it would work in BM.
As to rules in how it would work, are you allowing anyone to marry anyone, or only male-female marriages? Can you have multiple partners in marriage, or just one? Are we allowing divorces or is it for life?
