So what about ASCII control codes? They are non-printable characters that are part of Unicode, grandfathered in, yet aren’t part of any writing systems.

And home computers have had pictograms as part of their character set since the late 70s/early 80s. For example code page 437 (MS-DOS) had smilies, card suites, and other emoji. Likewise for the PETSCII (Commodore Pet) too.

And not just emoji’s, but full on drawing characters. In fact that was the only way to draw graphics on some early systems, such as Teletext, in the early 70s.

And then you have the question of what pictograms are part of writing systems. For example the media control symbols (play, pause, fast forward, etc). Or how about the fact that some emojis had been part of written text long before Unicode, in the form of “smilies”, eg :-)

I hope this illustrates that the problem was never an easy one to define boundaries for inclusion.