This did not aged well, seems like not only streamers getting access but actually they choose it randomly. I got it just yesterday although I am not any streamer at all
To shoot off any weird speculation:
Blizzard, family & friends and influencers & press may get Beta access.
If you’re not in that group you can opt-in for beta access and you may get invited eventually if the developers want to open it up for more people. It is not necessary to be a huge streamer personality or that you’re required to post only positive things to receive a beta invite.
No purchase necessary, the beta will flag your account for access.
Exemptions: When you’re penalised and your account is not in good standing you may not be allowed on the beta.
Still no beta access even with the invites that went out yesterday 
If I could give you mine I would. Constant disconnects (wow 51900319) and UI resets on gathering professions. It’s been open a month and still not working.