> modern currency symbols are already fast-tracked anyway For national currencies, perhaps. New national currencies aren't introduced all that often, and there

> modern currency symbols are already fast-tracked anyway For national currencies, perhaps. New national currencies aren't introduced all that often, and there is a lot of pressure to support them quickly as their use is often mandatory for anyone living in that jurisdiction. For new private currencies, including crypto-currencies, we don't see quite the same eagerness—the observation that new crypto-currencies were more likely to reuse existing Unicode symbols than invent new ones was a consideration in getting the Bitcoin symbol adopted, as they didn't want to open up the floodgates to large numbers of new currency symbols. The tag-based system offers a compromise. > and more than one currency symbols for given ISO 4217 code can exist so I don't think it would work That is a bit of a problem, but it could be handled with the variant selector codepoints, for example ¤MOP = MOP$, ¤MOP(VS1) = 圓, and ¤MOP(VS2) = 元, if the symbols have the same meaning. To save some space the VS could replace the end codepoint. For fractional units there could be a different prefix such as ¢ for 1/100 or ₥ for 1/1000 in place of the ¤, or incorporating one of the Unicode fraction codepoints for other ratios up to ⅞ (or ⅑ or ⅒). These would be rendered verbatim in the fallback version, like ¢USD.