If they announce that the next beta phase will be open then I'd consider that pretty big news!
I really don't think ANet would be hyping it this much if it wasn't big news. They don't seem like the type. And that G4 announcement just makes me think it'll be even bigger news. I don't think ANet would risk setting up the community for a big announcement and then release disappointing news.. not after impressing so many people. The fact that the press beta went so well is another thing that makes me think they'll give us a release month / date. I'm sure they had a date in mind, and a good impression would help solidify that.