Most likely this feature won't be added in near future because it requires a currency convertor first and secondly not all the payment gateways support all currencies and this could pose problems for existing installs.
I believe a single currency is enough, no need to make this area more complex than it has to be.
So we can create multiple currencies, but only the one selected as default will work, correct?
This shouldn't be that complex to implement. Just extra fields to enter the price for the plan for the activated currencies. No need for a currency convertor. Then when the customer signs up and in the customer profile we can give them the option to select their currency.
Obviously it will be your responsibility to have payment processors that support the currencies that you have available.
For my hosting company I have just USD, GBP, and EUR, and I adjust the price once a year. Usually currency fluctuations are not so big to update much more often. If I had Bitcoin that could be a problem