What limits small BWB-s is the wing thickness and headroom needed for passenger cabin.
B-2 has the headroom for cockpit, and wingspan and TOW capacity for a longhaul widebody.
Junkers/Mitsubishi G-38 had actually seats in the main wing and forward facing passenger cabin windows, but high drag was a problem. Burnelli had lifting fuselage and much thinner wings, but it was unpressurized.