According to the Wiki, the original UTF-8 proposal used up to 6 bytes.[1] But the Unicode standards people decided that 21 bit should be enough for everyone:
>Since the restriction of the Unicode code-space to 21-bit values in 2003, UTF-8 is defined to encode code points in one to four bytes, depending on the number of significant bits in the numerical value of the code point.
So, if they ever decide to use those extra two bytes, it will probably not be called UTF-8. Perhaps something like "UTF-8-MB-6".
>Since the restriction of the Unicode code-space to 21-bit values in 2003, UTF-8 is defined to encode code points in one to four bytes, depending on the number of significant bits in the numerical value of the code point.
So, if they ever decide to use those extra two bytes, it will probably not be called UTF-8. Perhaps something like "UTF-8-MB-6".
[1] https://en.wikipedia.org/wiki/UTF-8#History