adwsystems is right, I get the same feeling.
16 pins per MCP23017, 8 of them per slave and 64 slaves. That is 8192 pins.
Can you tell what your project is about ?
The most common way is to make something that is modular.
The I2C bus might not be the best choice for this. Suppose you want to reset all pins, that might take half a second.
Perhaps shift registers can be used or led strips or wireless modules.
Wiring 8192 pins can be a problem as well.