ISome of the more advanced features you requested (Multiple fills for example) while ideal for Pros, would confuse most home players completely, (About 95% of arrangers are sold into the home market, which is what manufactures have always designed them for) so while it could be done, sales wise it is probably not in the manufactures interest. (A module on the other hand is a completely different kettle of fish)
Bill
Most of us use Auto-fill, these days. Four fills, or sixteen, we still use the same four variation buttons to get fills (hit the same variation for fill-to-same). I don't think this would confuse the average user. And, while some of the things I ask for might be complex to make, in PRACTICE, they add no complexity to what the player does. Just gives more MUSICAL results when you do what you already do...