You will face challenges only when Bitcoin is banned or not legally recognised in your country.
I believe so too. Whether bitcoin will be classified in another category other than fiat money depends on the legal status it has in a particular country. There could be a reserve area as commodity as we can have gold, silver, oil, platinum and other metals. So Bitcoin can be categorized as digital assets and currency where it is accepted and adopted in a country.
But if it is banned in a country then it can't be included as assets to be part of the will, you could only convert to what currency known and accepted in the country.