When it comes to marriage, NPC's should generally line up with reality (nobles marry nobility, etc.), in order to keep the sense of immersion. So "marrying up" should be difficult (though not impossible for the highly charming, etc.). But reality should never bar an option from the player, especially not "marrying down." The point of open-world games like this is that you can write your own story, and there are plenty of roles that can be played in Bannerlord that do not involve being a noble anyway. If you choose to be a traveling merchant, or a highwayman that ends up wanted in every town, it's absurd that you should not be able to marry common characters or companions. Even if you are a noble, you should still be allowed to buck the rules if you really want to and marry a commoner. Maybe there can be some sort of influence penalty to keep things grounded. But either way, you should never take away the player's ability to choose for themselves, especially with such an important life choice.