I have a site that converts in both USD (banners) and EUR (shop).
It would be useful to be able to track conversions in different currencies for a site.
It would be, but currency conversion would be tricky (we'd have to call webservice to know about currencies), which is do-able of course, but not priority at this stage.
It would be better to maintain several balances, one per currency. Currency conversion doesn't happen in realtime, it happens when funds are transferred from one account to another.
This was also reported in https://github.com/matomo-org/matomo/issues/11854
We have a fairly pressing need to be able to track the currency with an eCommerce order. We receive purchases in many currencies on the site and at the moment they are all recorded in the Piwik site currency which causes large discrepancies with the actual value of the orders. I appreciate that to reconcile the different currencies would require some kind of an exchange rate but this should at least be exposed for development of a plugin if not in the core Piwik code.
Currently we implement a JS based workaround for Matomo only converting any shop currency into USD and firing eCommerce events to Matomo. Unfortunately it's not Matomo WooCommerce Plugin compatible :)