Is it possible to daisy chain several PICs via serin/serout statements?

[Jerson]

Typically you would do something like this using RS485 for control systems or DMX for lighting.

[Ioannis]

What you describe is something like what addressable led strips use, like WS2812B and APA102 to name a couple of these.

This, as you said can be made with arrays. It is the responsibility of the host device to send the appropriate number of bytes to the slave devices.

If the bytes are less the further devices will not get the data they need. If bytes are more, some will just get lost.

The downside as I see it, is the small speed you will obtain.

So, as Jerson noted, a protocol like RS485 is always better solution and more robust. Plus faster.

In any case if you want it simple, use Hserin/Hserout.

Ioannis