The current implementation recognises only legal tender as it fetches the currency list from the respective ISO 4217 standard as #4376 points out.

Is it on the roadmap to change this by for example defining a source of truth for applicable crypto short codes?

Right now there seems to be a lot undesired outcome variability.

The documentation says:

Use standard formats: ISO 4217 currency format, e.g. "USD"; Ticker symbol for cryptocurrencies, e.g. "BTC"; well known names for Local Exchange Trading Systems (LETS) and other currency types, e.g. "Ithaca HOUR".