User blog comment:Way2manybeer/Special war potentials/@comment-4822693-20130704131627/@comment-10961564-20130727193718

shinimagi were promoted to zero squad because they had given something new to soul society, had some special talent like reishi rich food or creating asauchi......it was never said that they had montrously high power levels but they must be very strong too as kirinji is faster than Suì-Fēng and a master healer

Yhwach did not said that yamamoto was more powerful 1000 years ago but that he was more ruthless and barbaric in his fights and did not care about anyone so he was more dangerous then...he had become soft now which is why Yhwach did not list him as a war potential

Urahara is also eligible to be counted as a special war potential as he surpasses Aizen in intellect and we haven't seen his bankai as well(which he achieved within 3 days like ichigo) so he might be one....shinji, shunsui and ukitake are others whose bankai are unknown and all are pretty strong as well