From wiki the original plan was for a next generation bomber (NGB) to be flying by 2018.
That was pretty ambitious and the program was changed to the current one.
According to defencenews.com the plane is supposed to use existing technologies, but
designed for accepting future ones:

ציטוט:

The program is targeting a production line of 80-100 planes. It will replace the fleet of B-52 and B-1 bombers. It will be stealthy, capable of carrying nuclear weapons, and optional manning has been discussed. A down-selection will be made this spring or early summer, with initial operating capability planned for the mid-2020s. Nuclear certification will follow two years after that.The target price, set by former Defense Secretary Robert Gates, is $550 million a copy. To keep the price down, the Air Force is looking to use mature technologies that are available now, rather than launching new developments. At the same time, the program will have an open architecture approach for future technologies.

With flying f35 and long use of the B2, stealth technology is mature. The same goes for avionics, especially after developing F35 and using the F22 in operations.

The design and development will not be cheap, and not all requirements are ironed out. But why would it be as complex as the F35?
Besides that the congress will not allow another delayed-hyper-expensive program like the JSF,
and both the big companies and the USAF do not want it as well.

Replacing the B1, B2, and B52 is serious business.

Sing while you may
- The Legendary Pink Dots