Korean doesn't use IDSes, it's a fixed algorithm (not specced by unicode, but a fixed algorithm) for combining jamos into a syllable block. Korean syllable blocks are made up of a fixed set of components.

IDSes let you basically do arbitrary table layout with arbitrary CJK ideographs, which is very very different. With Hangul I can say "display these three jamos in a syllable block", and I have no control over how they get placed in the block -- I just rely on the fact that there's basically one way to do it (for modern korean, archaic text is a bit more complicated and idk how it's done) and the font will do it that way.

With IDS I can say "okay, display these two glyphs side-by-side, place them under this third glyphs, place this aggregate next to another aggregate made up of two side-by-side glyphs, and surround this resulting aggregate with this glyphs". Well, I can't, because I can't say the word display there; IDS is for describing chars that can't be encoded, but isn't supposed to really be rendered. But it could be, and that's a vastly different thing from what existing scripts like Hangul and Indic scripts let you do when it comes to glyph-combining.

Jamo, Emoji (including flag combinators), Arabic, and Indic scripts all combine according on effectively per-character basis. There's not really any existing character that says "display any Unicode grapheme A and grapheme B in the same visual cell with A above B." The proposed additions to Egyptian hieroglyphs would be the first addition of such a generic positioning control character to my knowledge, albeit perhaps limited just to characters in the Egyptian Unicode repertoire.

Research on what to do vis à vis Mayan characters (including perhaps reusing Egyptian control characters for layout) is still ongoing, as is better handling of Egyptian.