Clif, I agree with you that it makes more sense to have the arranger software be the host. In a small way both Live - Styler (Soundfonts, B4) and OMB (sequencer) are moving in this direction. I may have inadvertently discouraged N. Stellberg to proceed along these lines by showing a screen shot of my live performance system. It shows Kontakt, B4, DecaBuddy, etc. loaded within forte and Live - Styler below it.

I contacted PG Music (BIAB) a long time ago about providing the option for real time arranger. They showed no interest. Similarily, Soundtrek is slow to update their JammerLive. I believe these people are not keeping up with the times or progress in computers, software and control surfaces. In fact, the big music companies (Yamaha, Roland, etc.) may see an opportunity slip away. It almost seems like the usual 'chicken & egg' syndrome!