After reading the three new chapters of the rules about the history, religion and the different kins I felt that it will be very hard to explain why dwarfs ever would be interested in being in a group with humans.
The other kins like elfs etc all had an possible explanation by providing example of why a PC would want to leave their home and mix with other kins instead of just killing them (or never leaving their home in the first place). But the different tribes of dwarfs all seem to have one thing in common, they hate humans.
Now, I and the players could of course make up a reason (e.g.g the PC hated the dwarfen society) but it would be nice to hear what other people think of this.