This threat should be in the temperate section; pawpaws are a temperate fruit, and there are several pawpaw threads there.
Many pawpaws are grown in zone 6, so that is not exactly news. I believe most of the big Kentucky growers are in zone 6b. It would be more interesting to find high-quality fruits from zones 5a and 5b growing in southern Michigan, northern Illinois, southern Wisconsin, and southern Ontario. Breeding seeds from those areas could possibly lead to some high-quality, ultra cold cultivars which could push their growing range farther north.
Unfortunately, the Twin Cities are zone 4b, too far north for pawpaws. That being said, microclimates could be created or found there which would allow some more naturally cold-hardy pawpaws from zone 5 to successfully grow.