Gem has it, others need to be able to read commercially available sample disks, like Akai format.

Karma has it, other could use real-time control of style parameters such as rhythmic complexity and swing factor. The Karma also has programmable chord buttons, and these might make sense on an arranger keyboard.

How about a USB port that allows any game controller to be plugged in and used as a midi controller? I am thinking mainly of the fighter aircraft joysticks, but heck, why not a steering wheel ?

How about mid-range keyboards with SmartMedia slots to hold 128 MB of styles and samples. Two slots should do. Floppies should be excluded or at least connected only via USB.

Instead of CDR, DVD-RW.