The Unicode Consortium doesn’t try to guess or predict which characters will be useful. Instead they go by which characters are actually attested in actual things humans have written. Thus we have characters like ꙮ U+A66E CYRILLIC LETTER MULTIOCULAR O, which was a doodle used by a monk in a single manuscript in place of a normal “o” in the phrase “many‐eyed seraphim” (“many‐eyed” has an “oo” in the middle in Slavonic). Note that the monk further illuminated this character with red ink; he was having some fun with it.
