"Is it advisable/wise/usefull to use a gate array for this?"

No !

Since you need already a CPU to control all these PCF8574, then it is the easiest way to arrange all these IOs already in software.

So there is no reason for using additional hardware.


E.g. I use lots of 74HC595 cascaded and every shift register correspondend with a byte in the 8051 bit space.

Then it is easy to change only this bit, which I want and send all bytes to the shift registers, where exact this pin was changed, which I want.


Peter