I think I can pick 10% rate of adoption so far. For now just few countries have made full move to adoption and also few institutions have allowed for bitcoin in their platform. Until a reasonable amount of countries starts proper adoption, hopefully from next halving.
I think 10% is the right answer in terms of mass adoption.
Remember that in order for something to be recognized, it must be categorized as legitimate in a country. If you want to see BTC being mass adopted worldwide, then it has to survive the issue of acceptability and absorption in a country. Though this may seem possible, I highly doubt that 100% mass adoption would happen even in the far future given the nature of BTC providing anonymity and freedom in transactions.
Remember that the government wants and needs control over its finances. They see cryptocurrencies as a threat to their absolute control which would hamper and reduce their effectivity.