In my naive opinion, a rack version is not going to sell well, if at all.
Considering that Casio's target market (and as a result to that, Casio's reputation) is leaning heavily into home players and beginners, they won't buy it.
Home players need "instant gratification" things. Plug and play, touch a finger or two in the left side of the keyboard and "wow, it's a Dm accompaniment, lets play some notew on the right side now".
Racks need setup, separate midi controllers, midi cables lying around, a more elaborate stand, 3 wall outlets (rack, speakers, contoller) or a T electrical adapter etc.

Imagine getting a nephew of yours a present like that:

"Here boy, is the rack unit, it is small and covered in buttons, it connects to the master keyboard via midi cables, and you can divide it into zones, and your mother is going to freak out seeing all those cables slithering on the floor, and by the way go fetch your speakers so we can hear what's going on".

True, it would be good to be able to choose a decent controller or add some new sounds to your existing setup without having to buy a new keyboard measuring three feet across, but people needing these are very few, I believe.

[This message has been edited by trident (edited 10-05-2005).]