I am sure that MIME works, and a lot of other schemes would work also,
like Otha-san's, or some ISO 10646 encoding
UTF-7 is just as bad as quoted printables.
Raw 10646, which includes bare NULL, won't pass any actual mail
transport.
That was why I created the mnemonic system some 4 years ago,
which has a smooth migration path from 7-bit ASCII thru 8-bit
character sets into 16-bit and even 32 bit encoding.
Mnemonic is a little worse than quoted printables in a sense that
they can't be viewed by those who don't support it.
Mnemonic is a lot worse than quoted printables in encoding length
and understandability.
Almost no one knows that "NASCULINE ORDIAL INDICATOR", whose shape is
superscript-o-with-underline, is 0xba of 8bit ISO 8859/1.
Masataka Ohta