The 4/3" sensor in the AF100 has slightly more than 4 times the area of a 2/3" sensor, and more than 6 times the area of a 1/2" sensor. Typically, the larger the sensor a lens has to cover w/o vignetting, the more it costs.
Motorized servo-zoom lenses are typically parfocal (they hold focus as the focal length varies), so they cost more than non-parfocal zooms, such as most DSLR zooms.
A parfocal, servo-zoom lens that covers the full m4/3 sensor will probably be very expensive; possibly far more than the cost of the camera body itself. Obviously the more a less costs, there will be fewer customers who will buy it.
If the AF100 proves popular it's likely at least one lens manufacture will eventually offer a parfocal, servo-zoom lens for 4/3".
However, given the cost of designing & producing such a lens, and the relative small initial size of the market, they may choose to wait to see how many they might sell before taking that gamble.
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