The invites are unlimited. It’s up to Google to shut down the invite system for everyone or not.
I don’t get it someone sent me an invite a while ago, I clicked it, and google just gave me the standard message of being full and just in beta
Also looking for an invite my email is peiman.anderw[at]gmail.com.
Thanks so much for the invites I received. It is cool to be getting in on what is sure to be a massive happening.