This suggestion would likely not be for the current BB, but rather a new standalone pedal or a feature in a future version of the BB.
This pedal/feature should be able to take a guitar input to generate an accompaniment of pads/strings, harmonising with the chords the guitarist is playing. The key for the song can be set before hand or the pedal could be intelligent enough to follow the chords being played.
This pedal could have a volume pedal to increase or lower the volume of the pads (or an input for a volume pedal). Or it can sense the volume/intensity of the guitar playing to move the volume up and down.
It could have a selection of built in sounds, and also the ability to input new sound patches for the pads. No programming would be necessary.
I presume technology for this is already available, seeing how pedals from TC Helicon and Digitech can take guitar and microphone inputs to generate three/four part vocal harmonies instantaneously. In fact, generating an accompaniment using built in pad sounds should be easier than creating voices and words.
I can imagine a singer/guitarist jamming or performing with a BB and ‘pad pedal’… awesome!!