Jim before you cut things up... I saw those photos on the thread about the Korg EK50. Are you sure you want that much "bulk?" With these conversions, it seems like much of the convenience/portability is lost.

The BK-7m (and the Ketron modules, if you're comfortable with a niche brand) are much smaller. Despite its compactness, the BK-7m has physical buttons for variations, fills, and one-touch settings. The new SD90 is a little larger. It also has a decent number of physical controls, while the SD40 makes do with a touch screen. (I'm not sure I would like that for triggering fills, etc., in real time; it might work fine but I haven't tried.)

IMO, arrangers are 85% software and 15% thoughtful ergonomics (although a good midi controller keyboard would have mappable sliders and pads for real-time use.) I agree that all the major brands should offer their MOTL, or even TOTL functionality in a compact module.