It's pretty clear that Boeing's new aircraft will carry side-by-side LD-3's. They are tired of ceding that point to Airbus with the 767. That feature was in the Sonic Cruiser design -- see the August 27, 2001 issue of AW&ST http://www.aviationnow.com/avnow/autonomy_samples/autonomysuggest/autosuggest.jsp?docid=13898&url=http%3A%2F%2Fwww.aviationnow.com%2Fcontent%2Fpublication%2Fawst%2F20010827%2Faw52.htm
, from which the following is snipped:
[John] Roundhill [vice president of marketing for the new aircraft at Boeing Commercial Airplanes] said lower-deck cargo-carrying capability is a key factor in determining a new aircraft's basic features such as range, payload and cargo hold cross section. The baseline design for the Sonic Cruiser has side-by-side LD3 containers under the passenger deck.
(The bracketed inclusions were taken from earlier in the article.)
This probably means a 2-4-2 layout, but perhaps it could be 2-3-2 if they use a double-bubble design and the composite structure allows higher volumetric efficiency. I think Boeing will try to find a way to get the cabin walls to be more vertical than the competitor, which to me suggests 2-4-2 and double-bubble. We'll find out in good time.
As for what the plane will look like, I believe someone already posted a link to http://seattlepi.nwsource.com/business/100543_sonic19.shtml
, which contains an artist's conception.