Depends what you mean by control, because it could be argued that they've already established control by taxing it. If you earn Bitcoin in several countries, you have to declare it as income tax, and I imagine there's a lot of people here on the forum that don't realize that they have to do that. So, technically they have already established a way of controlling it, and could actually introduce harsher tax rates for cryptocurrencies if they wish. That really is the only way of controlling it from their point of view though. They don't have any control on Bitcoin itself, only changing the laws around cryptocurrencies to suit them.

For example, I think they'll look at introducing specific cryptocurrency tax, instead of slapping it in the "tax income" bracket which includes all the income that you have made over a year. Although, I doubt it'll be any much strict that it currently is, and to be honest I don't think they are particularly concerned about Bitcoin at this moment. Its still very much a niche appeal despite its rising price.