In the past they did beta-invites in phases.
Some people (small and mid-sized streamers) reported that they got invites after the initial invite-phase of the current beta. But i think this is because they are streamers, content creators or from news/media.
I don't know how often new invites are sent, if they do the invites in phases this time. They could invite new players on a daily base or even manually depending on the state/process of development and testing.
Yeah they haven't said how the beta access is being rolled out. @neofrag is right about the streamers getting access slightly later on from what I saw too, but I haven't heard anything regarding normal users receiving beta access. I check it a couple times a day and hope for the best, but there's no telling how this'll go for the time being (unless I haven't seen something).