In the USAF magazine it was mentioned this month that the current thinking on the new bomber is that it would be a B -3 type aircraft (in other words - all new, not an upgraded version of a current bomber or commercial jet liner).
It is to be a manned, subsonic, medium bomber in a class between the proposed FB -22(bomber version of the Raptor wich was dropped) and the B-2. This is to be an interim, cost effective bomber to plus up numbers, since the 2006 quadrennial defence review stated a requirement to increase long range presicion strike by up to 50% by 2018.
Apparently the USAF wants to develop hypersonic technology further for a future bomber it wants to field in 2038.