The Korg series boards and modules were very successful and popular instruments (and most of them were black). The Korg i40M was introduced in the late '90's. Since the Korg introduced the PA series, I've been asking about a PA based arranger module. KorgUS flat out noted that there is NO MARKET for it, and KorgIt said pretty much the same thing. Therein, I believe is the answer.
But, you would think that the success of the Ketron modules would influence the 'no-market/no-product' view. I suppose the Korg marketing and R&D people have their fingers on the pulse of what SELLS.
Oh yeah, for me manufacturers can offer an interactive module with all the bells and whistles that the boards have.
Ciao,
Jerry