Problem is; looking at the artists conception in post 32, passenger cabin windows are shown extending back to where the fuselage tank is located.
That is correct for the original XB-70 design. But taking this design / concept into the 21st century using current state-of-the-art technology and scaling up the dimensions of the aircraft (within the current 80 by 80 meter airport limits) and enlarging the fuselage both in diameter and length, extending the passenger compartment all the way to the tail section would make it feasible. Fuel would be stored in the larger wing tanks, including the folding wing tips (which had no fuel tanks in the XB-70), and perhaps in the compartment that was originally designed as weapons bay. The original six YJ-93 turbo jets can be replaced by, say, four variable cycle engines or super cruise designs. Type of fuel is open for discussion.
The other design goal is minimum sonic impact on populated areas. Neither the SR-71 or the XB-70 could accelerate through Mach 1 (and on up to Mach 4.5) while in a vertical climb (70°+ pitch angle) at or above 45,000 feet. Not even close.
Concorde could reach Mach 2 only with a long, slow climb of about 20 minutes between ~27,000 feet and 51,000 feet, and a pitch of 4-5 degrees. The SR-71 had to level off at 33,000 feet and enter a descent (the "dipsy-doodle") to punch through Mach 1, followed by a Concorde-like climb/accleration at a constant 450 KEAS.
The XB-70 accelerated with wingtips lowered to mid-down position through the transonic region at 32.000 ft to M 1.5. Then the wingtips were lowered to their full-down position. M 1.5 was maintained to about 50.000 ft, and then varying rates of acceleration were applied until M 3.0 was reached at 70.000 ft. The best recorded time to M 3.0 was 25 minutes from moment of rotation at take-off.