Trading of anything including cryptocurrencies have always been subject to taxation. I've even seen up to 30% tax on trading profit. A lot of countries already have such taxes on cryptocurrency trading so it is not a new thing for "others to follow" after Slovenia does it since they are already behind themselves.
As for "transfers" you can't tax them at all unless they tax the businesses accepting bitcoin payments for each payment which is a different story.
I was also under the impression that most countries have a dedicated system in place specifically for cryptocurrencies, and if they haven't then any profits would be subject to income or capital gain tax, which might not be specifically for cryptocurrencies, but it would apply since you've made a profit. I think most countries have gone away from only taxing Bitcoin once it has been converted.
Also, if you mean transfers as in sending other users Bitcoin, then I wouldn't have thought they could tax that, since you aren't taxed that with fiat currencies. You should only be taxed on your profit; though how much completely depends on the country that you reside in.