Just because people are already doing confusing things with currency symbols doesn't mean we have to continue to do confusing things with currency symbols in the future.
Right! Just because a fringe groups like the US and Australia do with an overloaded currency symbol doesn't mean that Bitcoin needs to settle for such nonsense!
It's not a great solution though. With $ it works because in the majority of cases the context helps, for example in America they know it means USD, when I deal with people here in UK/Europe I know it means USD because of who they are, if I talked to an Australian I would know it means AUD (but would probably check with them).
However with Bitcoin, practically 0% of situations would be "that must mean bitcoins, not USD/other".