KC868-A8 PCB updated V1.5

[macek]

do you want a board only have input via PCF8574?

Yes, expansion board (with only input, input channel use optocoupler isolation,) for KC868-A8/A8S, like this - https://prnt.sc/UUCZXgM3QPQG

Can be installed above (on top) the KC868-A8/A8S board , there is a lot of space, something like - https://boneio.eu/img/boneIO_v0.2render.png

ESPHome support PCF8574 I/O Expander or MCP230xx I/O Expander. Kincony uses the PCF8574 expander everywhere.

8 channel in one i2c extend board?

It's the minimum, but it's better if the 16 channel will be.
16 connectors will fit on the side of the case.