I also think that EB does not need those characters. Playing MTW2 i have never used princesses because they can not really change anything. Priests are not suitable for EB period and merchants are useless because of things explained by MarcusAureliusAntonius.
Quote Originally Posted by Foot
Princesses are quite interesting, and with a modifiable diplomacy engine (to some extent) I'm hoping that these will add a little something something to the game.
I doubt that. In history there were many attempts to make diplomatic relations better this way, but often it was futile (Seleucids and Ptolemaids unsuccesfully tried to make more firm peace by marriages).