The more I look at Bohlen-Pierce theory, the absence of any discussion of utonal stuff strikes me as more and more peculiar. Even more so, very many of the 'major' scales include the utonal chord from the same root, and the 'minor' scales don't necessarily exclude the otonalities either.

Some have complained about modulation and such not being very clear in Bohlen-Pierce, and I wonder if this inclusion of both utonal and otonal structures for the tonic might be part of that? OTOH, borrowed chords in 12tet don't tend to cause big problems so ...?