If it's 10% instead of 1 in 20 million, then it should be a global phenomenon. It can't be hidden no matter how hard you try, because out of those 700 million there will always be some who likes to show it off. Hence my ideas, based on that simple observation, that come out of my head are as follows:

1. The specials will have to register to their respective national governments (with a detection test at least being in development), and they are supposed to be closely watched. Their whereabouts are always tracked, their words are always being listened, their Internet history is recorded, basically they are totally deprived of privacy under the pretext of "national security". Some countries, however, do not implement the same rules and become countries that the specials want to escape to, much to the dismay of other countries.

2. One of the specials created that fascist group that is starting to get support from an ever-growing number of specials as well as the normals, although the number of specials in the group will be of particular interest. The good guys (including anti-fascist normals) must stop the organization before the rest of the world couldn't match the group's might.

3. When two superpower countries (or perhaps three?) are locked in another cold war, the discovery of specials dramatically changes every nation's cold war playbooks. Countries begin recruiting specials, offering large payments to those specials for serving the country, and start developing war tactics and strategies around them. Once the situation escalates quickly, a new treaty was signed in an aim to reach a detente. Under the treaty, countries possessing such capabilities are obliged to "decommission" their specials, whatever that means.

As for the level of powers, having 700 million supermans will destroy the story before it even begins. Thus, I prefer that most specials will be able to give damages on a personnel level (i.e. going into a house barehanded and kill every (normal) people in it) without too much effort, but few will be able to give damages on a structural level (i.e. destroying the whole house itself and flattening it to the ground). One or two people can be more powerful than that, but there should be a lot of asterisks attached to that. All specials start out having only one power, although a handful of them will gain more as time progresses.