I did find some commentary, and I think it justly represents the piece, to my satisfaction at any rate: "...and the mystery only deepens in the proximity of an even bolder fragment for two pianos, in B[??] major (Fr 1782b; K. 375b) composed some months later: a Grave of extreme density followed by a Presto in triple time, whose opening theme is spiked with abrasive dissonance and quirky rhythmic displacement. It breaks off at the cadence before the dominant. The celebrated sonata for two pianos that Mozart actually finished (K. 448; K. 375a in Kochel, 6th ed.) is a very different kind of piece. For all the extroverted display of Mozart in D major, it yet promises less in the first half of its exposition than these two ambitious torsos, whose significance for the genre is eloquent even in their fragmentary state."
I did find some commentary, and I think it justly represents the piece, to my satisfaction at any rate: "...and the mystery only deepens in the proximity of an even bolder fragment for two pianos, in B[??] major (Fr 1782b; K. 375b) composed some months later: a Grave of extreme density followed by a Presto in triple time, whose opening theme is spiked with abrasive dissonance and quirky rhythmic displacement. It breaks off at the cadence before the dominant. The celebrated sonata for two pianos that Mozart actually finished (K. 448; K. 375a in Kochel, 6th ed.) is a very different kind of piece. For all the extroverted display of Mozart in D major, it yet promises less in the first half of its exposition than these two ambitious torsos, whose significance for the genre is eloquent even in their fragmentary state."
If anyone can find some commentary on this piece, let me know, because I can't really find any...