I think this is possible. But I believe the one that should be taxed are those exchanges as they are the ones at the receiving end of the transactions and the miners as well. If the governement will impose taxes while just holding coins certainly none will be left to be part of the community after being afraid of loses.
Every exchange is a registered company with the government. So they have to pay income tax as a normal company.
It's hard for the government to charge tax from crypto-traders since they are almost incognito
The exchange should be the one who's responsible in each transactions that we do inside our crypto business, just like what you have said most of the users are anonymous and they can hide their identity as what's the main goal of crypto so in behalf those registered exchange should take the responsibilities in order for government to acquire decent taxes as well from this market.