That is at least conceptually part of Unicode. You can encode „ü“ both as the character (one code point) and as „u“ followed by „modifier Umlaut“ (two code points).
Glyphs in fonts already make use of composite features (ü can be u + ¨, just the coordinates of the references). But readability of type can be complex, so I don't know if that's a viable solution to compose large-nonwestern fonts in a way that is natural to read. There may be very subtle differences that force the designer to decompose the parts and make modifications.
Ah! Knowing that, I bet that someone _could_ make a CJK font optimized for file size, which includes radicals by reference. It wouldn't work in every case, because radicals change size and strokes shift to make room for other strokes. In cases where the same radical appears in the same place, it seems like it would help.
But maybe that's not enough of a benefit unless there's also a way to say "okay you need to use this radical, but a bit narrower, but the strokes need to be the same width and not distorted".
The www.glyphsapp.com and www.fontlab.com font editor apps have "smart components" which do this. Sadly the OpenType format is developed very conservatively by Microsoft so these aren't part of the only widely supported font format today, despite recent additions to the format of run time interpolation technology.