Depends what year we base it on I would presume somewhere between 5 to 10% with less relatively each year but that does not include altcoin switches in the lower % range etc.
The point is that it is hard to measure hence its a shadow market and the percentage of the underground economy can only be guessed at not determined concretely.
So more than a nations average of 2-3% it still exists but in a lesser form than it used to.