I do remember reading that it is EB team's stance to not add merchants, priests, and princesses somewhere on this forum. The former two don't really have much significance, I understand that. But having a princess, from my short experience of M2TW, makes marriages infinitely more interesting. Playing as Parthia in EB2, I get asked if I want to bless a marriage of certain nobles for example. It really doesn't have any meaning to me since women in EB2 are just pictures with age written on them. The only significance of agreeing or disagreeing to 'bless' such marriages that I can think of is that I can deny a general from having children by not agreeing to have them marry.
Having a princess makes it much more interesting to marry generals in my experience. If you marry your general with a princess with bad traits which are usually acquired through your choice to wander her around, the general suffers negative traits. On the contrary, a princess with good traits helps the general as well. The important point I want to emphasize is that YOU get to control what happens to the princesses and that gives roleplay elements. Those princesses aren't just pictures you don't care about. Instead, they're actual family members that travel around conducting diplomacy affairs or marrying.
While I realize that princesses are not 'essential' per se in the game, they can add more immersion elements to the game. Isn't immersion a trait that EB2 developers are looking for? What are your thoughts on this? At the very least, I think it'd be nice if someone came with a submod that adds princesses. I'm guessing it's not too hard considering it's already in the M2TW engine.