A user on the Programming forum Keypad_I2C and Wire library problems with Due - #7 by system - Programming Questions - Arduino Forum is getting an error when trying to use the Keypad_I2C library with the Due.
I see that changes have been made to the Wire library and more importantly the only public facing function that had its signature changed is the empty constructor. It still exists in the AVR branch under hardware but has been changed for the SAM branch.
I was going to restore the empty constructor, compile, and test the code but the server for the 1.5.6-r2 beta is reporting a 503 error and I already deleted the only copy I had.