Just wait. It will happen sooner in some countries, later in others, but unfortunately it's almost inevitable.
Lots of predictions don't come true. The dystopian "A Nice Morning Drive" from 1973 turns into the Rush song "Red Barchetta" in 1980, and 40 years later, it hasn't happened.
The 20 year old prediction wasn't that in 20 years cash would be banned. It was that eventually it would be banned.
And yes, you can look no further than this thread to see that it is being either banned or severely limited around the world already.