I signed up for the beta on February 21st and got my invite last week at the top of May as they started letting folks in. From a graph I saw, they only had a couple hundred users til about April, then the May batch brought in another 50K (of which I was one). It's at 65K total now I think.

I have a negligible following on social media and don't know anyone over there so I don't think they're being cliquey with the invites.

To someone else's point, they're doing a lot of firefighting. When I got in, your followers list did an infinite loop, "hellthreads" were causing errors every time you viewed a reply, and content moderation was (and still is) constantly breaking (NSFW stuff keeps breaking through on their placeholder "what's hot" algorithm(. I was able to register @salesforce.herokuapp.com as my handle, etc.

I think it's a beta in the truest sense of the word and you'll probably get an invite soon.