Maybe it's a side-quel to fill in the gaps between 2.22 and 3.33? (like the content that was originally previewed at the end of 2.22)
Oh man, if only.
But yeah, I'm not really sure what to expect from 4.0 (or 3.0+1.0 or whatever, if they're the same thing now ), and if it's meant to be Rebuild's equivalent to EoE then it has a lot to live up to. Given how much 3.0 shook things up (for better or for worse) it should at least be interesting, though.
Also, I just really wanted to post this here: