The initial selection of players is quite small, but more will be added in time.
Blizzard has just announced that they've just sent out the first round of Beta invites for 'StarCraft II: Heart of the Swarm.' The initial selection of players included pro gamers, shoutcasters, press and contest winners, so the sampling is quite small. On the plus side, you're still able to get a look at the new game now.
The Beta invites did not include a nondisclosure agreement, which means pro players, casters and press can all record and stream the game as they like. So if you're hoping to get a look at the new units and some of the strategies that come along with them, a site like Twitch.tv is the place to go.
Blizzard has stated that more people will be let into the Beta as the time goes on.