Since you are asking again, it may seem you do not understand explaination above.
The Input in complementary metal–oxide–semiconductors as used in microcontrollers,
computer chps, and MCP23S17 port expanders,
is just a small pad of metal, on top of a layer of silicon oxide, which is basically a kind of glass.
These inputs use no current when the signal is stable.
The input act as a very small capacitor. Bonding wire, together with connection pad and traces inside the chip package and pin of the package, also contribute with a little capacitance.
Together, these are sometimes estimated to 5 picoFarad or less for each input pin.
Traces on your circuit board, and other wiring between devices, may contribute much more capacitance,
especially if there is long wiring between devices.
Twisted pair wiring as used in Cat5e Ethernet cable, is specified to have nominally 52 pF/meter capacitance.
So signaling quality depend much more upon length and layout of wiring and connections,
than number of devices connected. And frequency of signaling.
You may calculate rise and fall times of signals when capacitance of the whole connect,
and other properties are known.
You may calculate signal propagation based on transmission line theory,
Or you may observe the signals using oscilloscope.
How long time does it take for signals at the far end of the setup to reach stable level,
and for eventual reflections and overshoot to decay.
Inputs of microcontrollers and computer chips are sensitive to EMC and EMI interference,
so if there are long wiring, signal transcievers may still be a good idea.