That also doesn't change anything about bitcoin's fungibility as a currency. 1 bitcoin is always 1 bitcoin whether it is virgin coin, mixed coin or a "regular" coin when you want to use it as a currency not in some centralized service like for trading.
Bitcoin is
not fungible. There is already a pool that only mines "clean" transactions. Of course, it doesn't matter much yet for its small hash rate and the only block I know they've mined was not perfectly "clean" too (by their rules), but it can be a dangerous trend for 5 or 25 years from now.
Monero
is fungible, hence it's a problem for governments and it faces a lot more barriers Bitcoin had. It's still difficult to foresee what will its future look like, if any.