Do you have any links or information to back up this claim? It’s the first I’ve heard of this, and I can’t think of any obvious reason why Apple AI is going to be less secure than the rest of the OS.
That wouldn’t work because the emoji would then be too large compared to non-emoji characters. Line spacing would be messed up and the text flow would generally look bad. Emoji are supposed to be inline with text, not graphics that affect the text layout.