I think they announced that the V3 was also being showed at the bay area fair. That is what the email on april 29 says. So it may be that it's already done (I know one prototype was out in the wild already, although it was an early one), and that Part-daddy largely delegated it.
I think the V3 will have some really interesting features, but not a lot we don't already know about, and nothing that can't be backported.
New thing I think we'll see on the V3:
All metal hotend: we already know that the Eris has one, and that Part-daddy was working on the Rostock version of it's board and mount. IIRC, it's called the H280 or something along that line.
Modified bed attachment: The V3 prototype used Eris style clips to hold at least the glass on. They may either recess the heated bed (Like the eris, which will also keep crap out from under it), or use pylons to raise the clips, unless they have a different set of molds for the V3 clips than the Eris. I would personally like to see them move to a somewhat recessed bed, as well as slotting the holes on the Onyx, such that it can expand and contract somewhat, which should address two issues that exist. (And with the new shorter power supply, they have some more vertical room for that, if they tip the Rambo back more)
Acceloremeter probing: We know that a Rostock version is in the works, and that it's already working on the Eris. We also know that it will work on current gen RAMBO boards, since it works with a normal mini-rambo.
More angular: The prototype, again, had a more angular, truncated triangle form factor, and less of the curves. This is not anything but speculation, but it seems that SeemeCNC's aesthetic has been moving in that direction, and it's not a huge change (And eliminating those annoying bent panels would be nice)
Top/bottom agnostic design: Guano and Geneb discussed it here a while ago. The documentation will cover building it with the electronics up top, but you can (Or at least could at the time the thread was around) build it either way.
http://forum.seemecnc.com/viewtopic.php ... ver#p87640
Beyond that, I don't really know.