Assuming you are taking poses that already exist in game with other races, classes or weapons it should be pretty easy to implement. The problem would be unexpected model behavior or clipping of objects if you tried to hold a staff like another race holds their sword and it goes through your clothes or whatever.

It would be really hard to test every combination of race, class, weapon and gender to make sure everything behaves in a reasonable manner.

Edit: And by hard I mean time consuming.