Earlier quoted context omitted.
They should all be standardized under separate standards. You can call them "extended text", if you like. Mathematical notation isn't really supported by Unicode, either (just mathematical symbols), and that's fine. Math should have its own standard, and so should hieroglyphs, emojis, and musical notation.
What happens if you want to use two different extended text code points in one blog post? How would they interact? How do they avoid assigning the same codepoint to different symbols. How would browsers support this? What's the actual plan, not just a handwave? Do you think it'd be more efficient to have to support 6 different standards than one?
There are no codepoints if it's not text. How do you use codepoints for embedding a video or a picture on your blog? You don't! But, if you want to treat something as if it were text, then I suggested doing something similar to an XML namespace: "the next segment is hieroglyphics, you can get their glyphs from here, and these are their indices...". That "extended text" is still not text, and it still doesn't use any Unicode codepoints, but it can work according to similar principles.
> Do you think it'd be more efficient to have to support 6 different standards than one?
Then why don't we let the Unicode Consortium take over standardizing video or audio? If something isn't text, why is it standardized by a text standardization body?