Althougth the music for bandoneon is written on a grand staff, the treble clef is used just for the right hand and the bass clef for the left hand, therefore it would be useful if Dorico could show the notes out of range for each hand/staff and not only for the whole instrument. That is important when colaborating with people that are not familiar with the particularities of the instrument.
As a workaround (just for the low register of the treble clef of the bandoneon) i have added a bass oboe stave, copy there the music from the bandoneon treble clef, transport a octave down, so the notes under A (second ledger line) are shown as out of range. But than can be done only in a flow by flow basis, when you have many flows this workaround is time consuming.
For more info see http://www.bandoneon.co.uk/writing-for-bandoneon