I think design-your-own arrangers will never work or make it to market. What makes arrangers attractive is that they have all the controls and software needed to do the job - easily. Modules and software aren't as successful because the immediate, tactile interface is not there. Simplicity is essential. Look how we have moved back to more dials and controls because the multi-page menus were so cumbersome. Pianos and organs were/are popular because most of your time and effort is focused on playing. Drawbars are visual and tactile - virtual drawbars, duh!

Future arrangers will continue to be based on other synth/sound generating technology. The more you pay the more advanced the technology will be. Will an arranger ever be more advanced than a synth/keyboard? Why?