Before this discussion deep ends.
There is an early precedent, going back to the Euro sign, of Unicode
adding a new character instead of "repurposing" any existing character
that may seem to be unused.
The principle there is, that until a particular currency gets actually
created (or a specific symbol is officially adopted for an existing
currency) whatever character already exists in Unicode is for "something
else". It may be unclear precisely what it is to be used for, but it is
clear that it is *not* to be used for the new symbol.
So, there's absolutely no point in discussing whether or not some glyphs
should change - that's flat out.
This is different from using an existing character for a symbol that
does look like that character (e.g. if some currency were to adopt the
shape "$" as a symbol, then U+0024 would be the character to use,
irrespective of the name of the currency in question).
The identity of symbols, and that includes currency symbols, is largely
defined by appearance, much more so, than is the case for letter shapes.
Changing "glyphs" for a symbol really means changing its *identity*, and
that goes against the character code stability policy in a rather direct
way.
The reason why symbols are different from letters in this respect is the
fact that they don't have a word-context. When you see the symbol
displayed or printed, pretty much the only clue you have as to its
identity is the shape. That rather dramatically restricts possible
variations in appearance.
Still, modest variation is permissible, such as using one or two bars on
the Y (for Yen or Yuan) or one or two vertical strokes on the S (to make
a dollar sign). But assigning a newly introduced shape to an existing
currency symbol is out - you would change an unknown number of
documents, by changing the identity of a symbol that carries rather
strong semantics (i.e, is definitely not "decorative").
And it does not good to argue that this or that symbol are "practically
never used". Once something is encoded, neither you nor Unicode have any
control over where it is used, and by who, or for what purpose. All you
know for sure that whoever used it, could not have meant the new
currency (or newly designed symbol) so whatever assumptions they made
about the identity of the existing character *excludes* the possibility
that they might have meant the new currency or symbol.
And not only that, actual use of characters always exceeds the
information about such use. There was a time when it was thought nobody
had used certain Korean characters in any implementation because there
were barely any known implementations of Unicode in existence. Well, it
turned out that assumption was dead wrong. One of the lessons Unicode
learned from this and other early debacles is to be rather rigid about
the encoding stability policy.
So, forget about discussing existing characters. Every new symbol,
whether for new or existing currency will get its own character. And if
a currency, or symbol, is abandoned along the way by the sponsoring
nation, that's the cost of business.
A./
PS: none of what I discussed would prevent the correction of a definite
and outright mistake, where a wrong glyph might have made its way into
the character code charts - especially early in the lifetime of a
character. But there's wide gulf between admissible correction of
editorial mistakes on the one hand, and the disallowed re-purposing of
characters after the fact on the other.
