Personally, I would rather *not* see such a unification in this case.
The emoji thing is basically a dingbat, like the rest of the emoji set
(not in a pejorative sense ;-) but in the sense of being "just" a
general symbol, not part of a well-defined set with a specific purpose).
I think a unification with 1F4A4 might introduce some confusability. I
would advise encoding a new emoji eighth-note symbol and if you want,
make it a compatibility equivalent to 266A.
Which brings up another issue... I think a lot of these emoji that are
near duplicates of existing characters should have compatibility
foldings into other existing characters, or into each other. But I'm not
going to advocate any specific set, I'm just making an observation.
> We are not unifying Emoji symbols with specific scripts, like Egyptian
> Hieroglyphics, but would it be appropriate to unify with Musical Symbols?
> They are intended for fancy musical type-setting, but it does not seem
> unreasonable that some of them would be used in isolation.
Correct, but, when you say "in isolation", that generally would
mean in citation in texts that would have music as a topic and
which would expect the use of some dedicated musical font for
display of all the symbols.
> Specifically, I am wondering about
> U+1F4A4MUSICAL NOTE
> U+1D160 MUSICAL SYMBOL EIGHTH NOTE
> (Shift-JIS source separation prevents us from unifying with U+266A EIGHTH
I consider it a very poor economy to try to unify *one* symbol
out of 615 in a set of emoji with a symbol in the Musical Symbols
block -- largely because of the font support problem.
You are far, far better off having another musical dingbat in
amongst all the emoji dingbats, rather than depending on
loading what might be a specialized musical font that few
people would actually have installed just to get this
one symbol displayed correctly.
Just make the U+1F4A4 glyph have a whimsical, emoji-appropriate,
dingbatty shape that is *inappropriate* for formal musical
typesetting, and people will not worry about its non-identity