The ideographic description characters do provide a way to describe how to map radicals into characters, but don't actually provide rendering in such a manner.
There is active discussion on actually being able to build up complex grapheme clusters in such a manner, because it's necessary for Egyptian and Mayan text to be displayed properly. U+13430 and U+13431 have been accepted for Unicode 10.0 already for some Egyptian quadrat construction.
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.
There is active discussion on actually being able to build up complex grapheme clusters in such a manner, because it's necessary for Egyptian and Mayan text to be displayed properly. U+13430 and U+13431 have been accepted for Unicode 10.0 already for some Egyptian quadrat construction.