I think the future of the arrangers lies in the shifting of its functions to the computer (or integrating a computer into the keyboard.)
The concept (in current terminology) would be a dxi or vst that would sit between the keyboard and a sequencing program like SONAR.
The dxi would be responsible for chord recognition and manipulating the incoming stream from a keyboard which would have the raw capability of assigning all sixteen midi channels to instuments. It would define a split in the keyboard, and would provide a way of designating measures in SONAR as "accopaniment" measures, transposing them according to the chord rec. AI in real time.
There are already samplers that can stream large samples from discs effortlesslly. VSampler and Reaktor are example dxi's for SONAR, although they can't separate the MIDI stream into individual tracks live (yet - I'm bugging them about it....:-)
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