Ketron already do an arranger module called the SD3.

Designing, Developing, Tooling and Producing a new arranger module is just as expensive as a new arranger keyboard, therefore while bringing out a module of an existing arranger may be economically viable, (There is still all the tooling costs to take into account) no manufacture will make one unless they are 100% sure that they can easily re-coup their costs.

Best way to bring it forward is to petition the manufactures so that they know the demand is there.

Bill