The cost of copper really pushed the price up of foil inductors over the last year and a half, and restocking would have forced us to raise the price of the upgrade even further. And we felt it was better to drop this upgrade for the time being, especially since it had already doubled from $125 to $250, and we would have to raise the price to $300+ to match the current prices.
We still plan to keep the foil upgrade for Oticas & Extremes, since the values are smaller than on the Studios.