[kccqzy]

Well languages and conventions change. The € sign was added not that long ago and it was somewhat painful. The Chinese language uses a single character to refer to chemical elements so when IUPAC names new elements they will invent new characters. Etc.

[extraduder_ire]

Does unicode have space set aside for those new symbols to slot into? I know it's very rare, but it could get messy.

[account42]

Unicode is already messy. Chinese characters especially so due to han unificiation.