Currently this isn't tested, I am making the prototype at the moment and am waiting on the ATTiny controller to arrive. I have prototyped the audio switch IC side and that is working well (it is 'controlled' directly by a rotary switch I had laying around with a couple of diodes to have the 4 throws into 2 bits).
Once I have the ATTiny chips I will breadboard them to check function and that the program works right.
On the note of the program. I am hoping that it will be able to switch between operation modes automatically. When it is used with a rotary switch (SP4T) one of the inputs will always be held low, so when power is applied the software checks and if none of the inputs are low it will activate the button/I2C mode, otherwise it will be the rotary switch and the I2C mode is turned off.
The I2C address by default has two options, selectable from a solder jumper on the board, the options are 0x2e and 0x2f. They can obviously be changed in the program.
There is also a header for being able to program the chip - again I am hoping it will work and will be tested because I have to program it somehow!