You opt in by posting here that you want in. I will go back through this thread when it comes to creating the initial chain state and add everyone's account at the beginning. 

Getting a sign up in the initial time between it going live and the first exchangers operating to pay for a new account may take a little while to organise. I will be designing a 'fremium' signup account type, that hopefully I can put in the initial state of the system, that will have a special flag that indicates it has certain limitations, like not being able to have Stake delegated to it, and other features, which are yet to be determined. 

We don't want to make it easy for the trolls to get in and not be subjected to the community opinion about their activity on the new platform. Trolls who attract flags from other users, in this platform, will have their vote power limited by their reputation being hammered down. This is a anti-troll countermeasure that will be in the initial rollout.